The market expected a fall
London’s market was supposed to fall. Futures traders expected it. The forecast came before trading opened on Monday morning, with investment platform IG predicting a drop for the UK’s blue chip index. This pessimism followed a difficult end to the previous week. The FTSE 100 suffered heavy losses on Friday. It closed 1.5 per cent lower. The logic for another day of decline seemed solid, especially as falling oil prices were seen as a negative weight on the entire index, suggesting Monday would continue the downward trend set on Friday.
The market did not fall. It climbed. By the close of trading on 21 September 2026, the FTSE 100 index had defied all the early morning predictions from City analysts. It ended the day up 79.88 points. The final figure was 10,739.01. This represented a climb of 0.8 per cent, a stark and surprising reversal from the 1.5 per cent loss recorded just one trading session earlier. The predictions were wrong. The day’s result was a complete inversion of what had been anticipated only hours before.
The narrative before the 08:00 bell had been consistent. City AM’s live coverage captured the mood, reporting that the index was set to drop from the start, extending the pain from Friday into the new week. This was the consensus view. The analysis was based on the simple and usually reliable observation that falling oil prices would hit the share price of energy giants. Because these companies are so large, their performance often has a substantial influence on the direction of the entire FTSE 100. A bad day for them often means a bad day for the index.
But not on Monday. Something else happened. The negative sentiment that was supposed to drag the market down was instead overwhelmed by a contrary force, an optimism that spread through almost every other sector. This created a clear split. The question was why. Understanding the day’s trading means understanding why bad news for some companies was interpreted as very good news by nearly everyone else. The puzzle was not simply that the initial forecast was incorrect, but that it was incorrect by such a significant margin and for such a counterintuitive reason.
Oil prices are a double edged sword
Oil prices are a double edged sword. For a company like BP or Shell, the global price of crude is fundamental to its existence. They sell oil. Their revenues are directly linked to its market value, meaning a dip in the per barrel price translates immediately into lower income and reduced profit forecasts. Investors know this. They act on it. A fall in the price of Brent crude is therefore a direct threat to the share price of any company whose primary business involves extracting hydrocarbons. Their fortunes are tethered to it. The entire business model, from exploration in the North Sea to refinement in vast coastal facilities, is built on the assumption that the final product will sell for a profitable sum. When that sum shrinks, so does the company’s value. It is a simple, brutal and unavoidable calculation.
But the FTSE 100 is not just an oil index. The vast majority of its constituent companies do not sell oil. They buy it. They consume it in huge quantities. For these businesses, oil is not revenue. It is a cost. A fall in the price of oil is therefore not a threat but a relief, a welcome reduction in their single largest and most volatile operating expense. Think of an airline. International Airlines Group, the owner of British Airways, must purchase millions of pounds worth of jet fuel every week just to keep its fleet in the air. A sustained drop in the price of oil means the cost of running the 07:00 flight from Heathrow to New York JFK falls, creating a potential for wider profit margins that investors find extremely attractive. The same logic applies everywhere.
This effect ripples through the economy. It touches almost every sector. Supermarket groups depend on vast logistics networks, fleets of refrigerated lorries that travel thousands of miles every single day, and the fuel for those lorries is a major component of their overheads. Cheaper diesel means cheaper deliveries. It means lower costs to run their stores. For manufacturers, whose factories consume enormous amounts of energy to power machinery and keep production lines moving, a lower oil price offers a direct boost to their bottom line. For these businesses, a falling oil price is a gift. It is a direct subsidy. Investors saw this possibility on Monday and bought into the companies they knew would benefit the most from cheaper energy.
This is the central conflict that explains Monday’s trading. The damage was contained. It was limited to the energy giants and their associated service companies, which are large but few in number. The benefits, however, were diffuse. They spread across dozens of other blue chip firms, from aviation to retail, haulage, and industrial production. The collective optimism about lower operating costs for the many outweighed the specific pessimism about lower revenues for the few. The mathematical composition of the index, which is weighted by market capitalisation but populated by a diverse range of industries, meant the positive sentiment had a broader base. More companies stood to gain than lose. That is why the index climbed. The market acted on this division. What spelled trouble for BP and Shell was seen as an opportunity for almost everyone else.
The view from Washington and Tehran
The trigger was diplomacy. Or the rumour of it. Monday’s market movement was not caused by a change in industrial output or a sudden discovery of a new oilfield in the North Sea. It was driven entirely by events in Washington and Tehran, where the possibility of a political settlement began to take shape. This is about international relations. It is about sanctions. The mere whisper of a deal between the United States and Iran was enough to redraw the financial mood in London, shifting billions of pounds based on what might happen next, not on what has already occurred. The market reacted to a potential future. It priced in hope. Nothing is certain.
For years, Iran’s vast oil reserves have been partially locked away from global buyers. A severe and complicated regime of American led sanctions has prevented the country from exporting its crude oil freely, a measure intended to apply diplomatic and economic pressure on the government in Tehran. This policy effectively removes millions of barrels from the world’s daily supply. It constrains the market. The hope that sparked Monday’s activity is that these sanctions could be eased. A political deal would be the key. If diplomats can find an agreement, those restrictions could be lifted, allowing Iranian oil to flow back into the international marketplace without penalty.
That is the mechanism. It is a simple question of supply. The sudden reintroduction of a major producer like Iran would significantly increase the amount of oil available for purchase globally, and basic economics dictates that when supply rises while demand stays the same, the price must fall. Traders do not wait for a formal announcement. They cannot. They act on the probability of an event, and the prospect of a successful negotiation was judged high enough to warrant selling oil futures, pushing down the price. The market is a forecasting machine. It made its calculation. What investors saw was the potential for a fundamental rebalancing of global energy, a shift that would make the world’s most important commodity cheaper for everyone except those who produce it.
This optimism remains fragile. It is built on tentative reports. It is based on a possibility, not a reality. The path of diplomacy between the United States and Iran is notoriously difficult, filled with historical mistrust and the potential for talks to collapse over the smallest detail. A breakdown is always possible. A single hostile statement or a failure to agree on a minor clause could reverse the entire process, causing the price of crude to spike just as quickly as it fell. The market’s confidence is conditional. It is a bet on a successful outcome. It hangs on the words spoken by negotiators in rooms far away from the trading floors of the City.
Winners and losers on the day
The consequences were not felt evenly. Not at all. For two of the FTSE 100’s largest companies, the news from Washington and Tehran was unambiguously bad. BP and Shell are oil producers. Their entire business model is built on finding crude oil, extracting it from the ground, and selling it for the highest possible price on the global market. When that price falls, their revenues fall. Their profits are squeezed. Their shares become less valuable. It is a simple and brutal equation. Monday’s trading reflected this reality perfectly. Investors, anticipating lower income for the energy supermajors, sold their shares. The companies are so large, their weighting so significant, that their decline should have dragged the entire index down with them, just as the early morning forecasts predicted. It was a logical expectation.
That did not happen. It did not happen because for almost every other company listed on the exchange, oil is not a source of revenue. It is a cost. It is a vast, essential, and often volatile expense that eats into profit margins and complicates financial planning. For these businesses, the prospect of cheaper oil was a cause for celebration. A sudden drop in the price of crude is a direct, immediate, and welcome reduction in their operating expenditure. Consider the airlines. A company like International Airlines Group, the parent of British Airways, spends billions of pounds a year on jet fuel, an expense that can account for more than a quarter of its total costs and whose price is directly tied to that of crude oil. Cheaper fuel means cheaper flights. Cheaper flights can stimulate demand. It means the difference between profit and loss. The same logic applies right across the economy.
It helps almost everyone. Take the haulage industry, the network of lorries and vans that transports goods from ports to warehouses and from warehouses to shops. Diesel is their lifeblood. A lower price at the pump translates into a lower cost for every single journey made by a Tesco truck or a Royal Mail van. Manufacturing plants that rely on petroleum derivatives as raw materials or use significant energy in their processes also see their costs decrease. Even retailers benefit from the secondary effects, as lower transport costs for their suppliers mean they can potentially hold off on price rises for consumers, who in turn might have more disposable income if they are spending less to fill up their own cars. The gains were widespread. They were powerful. The collective sigh of relief from the dozens of companies that are net consumers of energy was strong enough to completely overwhelm the negative pressure from the two oil giants. The market had found a new direction.
A foundation built on hope
The foundations are fragile. Monday’s optimism was built on little more than a rumour of progress between Washington and Tehran, a whisper of diplomacy that traders magnified into an 80 point gain for the FTSE 100. Nothing is certain. The market is not reacting to a signed treaty or a public handshake. It is reacting to a possibility. A complex chain of events must unfold perfectly for Monday’s logic to hold, beginning with successful negotiations, continuing with a verifiable agreement on Iran's nuclear programme, and ending with the complete lifting of international sanctions that would finally allow Iranian crude oil to flow freely onto global markets. Not one of those steps has been taken. The entire structure of the day's gain rests on the hope that they will be. It is a speculative bet. A very large one.
Diplomacy can collapse. It often does. A single misspoken word, a shift in domestic politics in either the United States or Iran, or a simple failure to agree on technical details could derail the entire process in a matter of hours. The market's reaction would be swift. It would be brutal. The very same logic that propelled the wider market upwards on 21 September would then work viciously in reverse, as the prospect of cheaper energy evaporates and the spectre of sustained high oil prices returns to haunt company balance sheets. Oil prices would rebound. The gains seen by airlines like IAG and the broad basket of industrial and retail stocks would be erased, potentially dragging the entire index back down below the level where it started the week. This is the immediate risk. Investors are now exposed not only to economic data and corporate earnings but also to the unpredictable outcomes of closed door negotiations thousands of miles away. The market is now a geopolitical analyst.
The upside, however, is substantial. If the talks succeed and a durable agreement is reached, the effect on the British economy could be transformative, extending far beyond a single day's trading activity on the London Stock Exchange. A sustained period of lower oil prices would act as a powerful economic stimulus. It is the equivalent of a tax cut for almost every business and household in the country, reducing the cost of production for companies and lowering the price of petrol for consumers. This would directly combat inflation. The Bank of England's Monetary Policy Committee, tasked with keeping inflation near its two per cent target, would find its job made significantly easier, creating space for a more accommodating stance on interest rates. For the companies on the FTSE 100, this is the best of all possible worlds, a scenario where their input costs fall, consumer spending power rises, and the cost of borrowing remains low. The rally would have legs. It would have a solid foundation.
For now, the market waits. Every news bulletin will be scrutinised. Traders will monitor the movements of diplomats and parse the language of official statements for any hint of progress or breakdown. The price of Brent crude oil is the key metric. It has become a real time barometer of geopolitical sentiment, its fluctuations reflecting the shifting odds of a deal being made. The fate of the FTSE 100, for the next few days at least, has become detached from its fundamentals. It is a hostage to fortune. It is a hostage to hope. A successful outcome could lock in the gains and propel the index higher still. A failure will bring a sharp and painful correction. The market holds its breath.
Sources. Evening Standard: FTSE 100 climbs as oil prices dip on US-Iran talks hope. City AM: FTSE 100 Live: Stocks to drop after falling oil prices weigh on BP and Shell.
Analysis. Drafted with AI assistance from the sources listed above and reviewed by an editor before publication. Jnews links to the organisations it writes about.
