Tuesday's sell-off hit London's largest companies much harder than its mid-caps, and the explanation lies largely in what each index contains.

On a day when the FTSE 100 suffered its sharpest one-day fall in a month, the FTSE 250 held up noticeably better. The Blue-Chip index closed on Tuesday 3 November 2026 at 10,638.43, down 122.90 points or 1.14%. The mid-cap index, by contrast, finished 0.5% lower at 24,674.91. In percentage terms, the FTSE 250's decline was less than half the size of its bigger sibling's.

That gap is not a coincidence. The two indices are built from different kinds of companies, and Tuesday's selling was concentrated in exactly the sectors where the FTSE 100 is most heavily exposed. Looking at where the losses fell, and at one standout mid-cap gainer, helps explain why London's two main benchmarks told such different stories on the same afternoon.

Different indices, different ingredients

The FTSE 100 contains the largest companies listed in London by market capitalisation, and the FTSE 250 contains the next 250. Both are weighted by market value, which means the biggest constituents have the greatest influence on daily moves. In the FTSE 100, that includes global miners, multinational banks and large consumer groups whose fortunes are often tied to Commodity prices, international Demand and currency swings rather than to the UK economy alone.

The FTSE 250 is commonly regarded as having a stronger domestic tilt, with more companies whose Revenue comes largely from the UK. It also tends to have a broader spread of sectors without the same concentration in a handful of very large resource and banking groups. On a day driven by falling metal prices and nervous bank trading, that mix offered some protection.

None of this means mid-caps are immune to broad sell-offs. Companies with heavy domestic exposure can be more sensitive to UK interest rates and economic data, so a rate decision or a weak growth figure can affect them more directly. On Tuesday, however, the themes in play mostly hit sectors where the FTSE 100 carries far greater weight.

Where the FTSE 100 took its hits

The biggest pressure on the FTSE 100 came from the resources sector. The FTSE 350 basic resources index fell 2.6% as copper dropped to a multiweek low, and midday reports said industrial metal miners had sunk to their lowest in almost four months. Antofagasta (LSE:ANTO) fell 3.5% and Glencore (LSE:GLEN) lost 2.8% by the close, while Anglo American (LSE:AAL) was down about 2.8% at midday. Precious metal miners, including Endeavour Mining (LSE:EDV), also declined, with the group down about 2.7% at a three-month low around lunchtime.

Banks were the second major drag. The FTSE 350 banks index fell 1.6% ahead of the Bank of England's rate decision on Thursday 5 November. HSBC (LSE:HSBA) dropped 2.0% and, because of its size, was the single largest approximate drag on the FTSE 100 in points terms.

Company results added to the damage at the top end of the market. Associated British Foods (LSE:ABF) was among the FTSE 100 fallers, closing down 2.2% after forecasting lower annual profit, and Coca-Cola Europacific Partners (LSE:CCEP) fell 2.1% after flagging cost pressures. Rolls-Royce (LSE:RR.) and RELX (LSE:REL) were each down more than 1.6% at midday, with no company-specific reason given. Because so many heavyweight names fell together, the cumulative effect on the FTSE 100 was considerable.

A mid-cap standout

The FTSE 250 also had a notable boost from within. Drax Group, a FTSE 250 company rather than a blue-chip, rose 6.6% to become the top mid-cap gainer after announcing a data centre Partnership with Brookfield Asset Management and Radiant. A single performer cannot offset a broad market decline on its own, but on a day of limited losses it helped cushion the mid-cap index.

Within the FTSE 100, Hiscox (LSE:HSX) provided a similar bright spot, rising 2.9% after reporting a 9.5% increase in nine-month premiums. Hiscox has been a member of the FTSE 100 since 23 September 2024, a reminder that the boundary between the two indices shifts as companies grow or shrink.

That boundary is reviewed every quarter. In the September 2026 review, easyJet and Ithaca Energy joined the FTSE 100, while Entain and Persimmon left, with the changes taking effect on 21 September. Since then, Balfour Beatty has replaced Schroders and WPP has replaced Beazley, effective 1 October 2026.

Those changes illustrate how fluid the composition of each index can be. A company's move between the FTSE 250 and the FTSE 100 can alter the sector balance of both, and with it the way each index behaves on days dominated by particular themes.

The next quarterly review is already scheduled. FTSE Russell will use Market Capitalisation data as at Tuesday 1 December, announce the results on Wednesday 2 December after the UK close, and implement any changes from the open on Monday 21 December 2026. Companies near the cut-off points may attract extra attention as those dates approach, since index inclusion or exclusion can affect demand from funds that track the benchmarks.

Key dates to watch

Thursday 5 November:Bank of England MPC decision, with a 25bp rise to 4% widely expected.

Thursday 12 November:ONS first quarterly GDP estimate for July to September 2026 (7:00am), relevant to domestically focused stocks.

Tuesday 1 December:FTSE Russell December review market-cap data cut-off.

Wednesday 2 December:December review announcement, after the UK close.

Monday 21 December:December review changes take effect at the open.

The bottom line

The FTSE 250's milder 0.5% fall on Tuesday reflected the make-up of the two indices as much as the mood of the market. The FTSE 100's heavy weighting in miners and large banks left it exposed to a copper slide and pre-decision bank selling, while results from ABF and CCEP added further pressure. The mid-cap index, with its different sector mix and a sharp rise in Drax, escaped more lightly. Upcoming domestic data and the December index review may offer further clues about how the balance between the two benchmarks evolves.