FTSE 100's best week in six months — and what the rotation into defensive stocks teaches you

TL;DR: A global sell-off in AI-linked technology shares pushed investors toward safer, steadier companies instead. Because the FTSE 100 has relatively few big tech names, it benefited from that shift and posted its best week since April — even though some sectors within it, like banks, fell. This is called sector rotation, and understanding it will help you make sense of weeks when the market moves in ways that seem to contradict the headlines.

What actually happened

According to Reuters reporting carried by Yahoo Finance, the FTSE 100 closed 0.38% higher on Friday 16 October 2026 at 10,881.90 points, taking its gain for the week to 3.1% — the index’s best weekly performance in six months. The move was confirmed by a second independent report, from Investing.com, which noted the index was also weighing Middle East tensions and elevated oil prices during the same week.

What stood out was not the overall number, but which shares drove it. Over the week, the beverages sector rose 7.8%, medical equipment and services gained 6.9%, and personal goods climbed around 7.2%. Individual names told the same story: cigarette maker British American Tobacco rose 2.1%, Johnnie Walker owner Diageo gained 1.9%, and defence contractors BAE Systems and Babcock International rose 2.6% and 3.6% respectively. Meanwhile, UK banking shares lagged behind on investor worries about a possible tax increase on banks in the government’s upcoming Budget.

The real driver: an AI stock sell-off elsewhere

The reason this rally happened had very little to do with the UK on its own. Through the same week, markets worldwide saw a pullback in shares linked to artificial intelligence — chipmakers, data-centre operators and software firms that had driven much of the past year’s gains in US and Asian markets. Investors grew uneasy about the sheer scale of spending on AI infrastructure, rising competition from Chinese technology firms, and uncertainty about when, or whether, that spending would pay off in profits.

When investors become nervous about one part of the market, they do not usually just hold cash — they often move money into companies they see as lower-risk. That is exactly what happened here: money flowed out of AI-linked growth stocks and into defensive sectors, industries whose sales hold up reasonably well regardless of economic conditions.

What makes a stock “defensive”?

A defensive stock belongs to a company selling things people need or want to keep buying no matter what the economy is doing. Classic examples include:

• Consumer staples — food, drinks, tobacco and household goods (people keep buying these even in a downturn)
• Healthcare — medicine and medical equipment (illness does not pause for a recession)
• Utilities — electricity, gas and water (essential, regardless of the news cycle)
• Defence — government military spending tends to be stable and often rises during periods of geopolitical tension

Compare that with cyclical stocks — companies like AI chipmakers, whose fortunes rise and fall with economic cycles and investor appetite for growth. When sentiment wavers even slightly, cyclical and growth share prices can fall sharply, because so much of their valuation was built on optimism about years to come rather than on profits already being earned today. Our earlier guide on cyclical vs defensive stocks covers this distinction in more depth if you want the fuller picture.

Why the FTSE 100 specifically benefited

This is the part that often confuses people new to investing: how can one country’s stock market rise while a global sell-off is happening? The answer lies in what each index is actually made of. Unlike the US Nasdaq or other tech-heavy indices, the FTSE 100 has relatively little exposure to large semiconductor and AI software companies. Its biggest constituents sit in banking, energy, mining, consumer goods, healthcare and defence instead.

So when a sell-off specifically targets AI-linked shares, an index with very few of those shares in it is simply less exposed to the damage — and if investors are actively rotating money into the defensive sectors that index does have a lot of, it can rise even as other markets fall. UK large-cap exchange-traded funds reportedly attracted their largest annual net inflow since 2020 this year, a sign that some of that rotation has been flowing specifically toward London-listed shares.

An average can hide a very mixed picture

It is worth remembering that an index like the FTSE 100 is an average of 100 companies. A rising index does not mean every share in it went up. Bank shares actually underperformed that week, weighed down by concerns that the Chancellor’s autumn Budget could include a new tax on banking profits. So in the same week, you had healthcare, defence and consumer staples shares climbing strongly while banking shares went nowhere or fell — and the overall index number only tells you the net result of all of that pulling in different directions.

This links closely to the idea of a stock market sector: grouping companies by what they actually do helps explain why an index can move in ways that a single headline figure does not capture.

What this means for your portfolio in the Challenge

If you are holding a mix of shares in the Student Investor Challenge, a week like this is a useful real-time lesson in a few ideas worth remembering:

1. Sentiment can shift sectors faster than it shifts the whole market. Watching only the headline index number can hide big moves happening underneath it. If you hold shares in a specific sector, track news about that sector specifically, not just the overall market mood — see our note on market sentiment for more on how that works.
2. Diversifying across sectors smooths out these swings. A portfolio holding only AI-linked growth shares would have had a rough week. One spread across defensive and growth sectors would have felt the rotation far less sharply — the core idea behind diversification.
3. “Risk off” moves do not mean investors are leaving the market. They often just mean money is moving to a different part of it. Recognising where that money is going can tell you a lot about what investors are worried about.
4. Volatility in one sector is not the same as volatility in the whole index. Our guide on what volatility actually is covers how to tell the difference between a shaky stock and a shaky market.

None of this is a signal to chase defensive stocks or avoid tech shares — markets rotate back and forth constantly, and a sector that is in favour one month is often out of favour a few months later. The lesson is not which sector to pick. It is learning to read why an index moved the way it did, rather than just watching the number go up or down.

FAQ

What is a defensive stock?

A defensive stock belongs to a company whose sales do not change much whether the economy is booming or struggling — think tobacco, drinks, household goods, healthcare and utilities. People keep buying these things in good times and bad, so profits tend to stay steadier, which investors often reward with steadier share prices when markets get nervous elsewhere.

What does ‘sector rotation’ mean?

Sector rotation is when investors move money out of one group of industries and into another, usually because their view of risk or the economic cycle has changed. In October 2026, money rotated out of AI-linked technology shares and into defensive sectors such as consumer staples, healthcare and defence, which is why those sectors rose even as broader confidence in tech wavered.

Why did the FTSE 100 do better than markets with more technology stocks?

The FTSE 100 has relatively little exposure to large technology and semiconductor companies compared with indices such as the US Nasdaq. Its biggest companies sit in sectors like energy, banking, consumer goods, healthcare and mining instead. When an AI-linked sell-off hits tech-heavy markets hardest, an index with less tech weighting can hold up better, or even rise, because the shares being sold are a smaller part of it.

Does a strong index week mean every share in it went up?

No. An index average can rise even while some sectors within it fall. In this case, banking shares in the FTSE 100 lagged behind on worries about a possible UK Budget tax increase on banks, even as consumer staples, healthcare and defence shares climbed strongly enough to lift the index overall.