Why the FTSE 100 is a poor barometer for the health of the British economy.
In short: The FTSE 100 is the UK's most famous stock market index, yet it is a surprisingly weak indicator of domestic economic performance. Because its constituents are predominantly global companies, the index is more sensitive to international currency fluctuations than to the actual state of business within the United Kingdom.
Launched on 3 January 1984, the FTSE 100 was designed by the London Stock Exchange to track the 100 most highly capitalised blue-chip companies. It quickly became the primary gauge of market sentiment, bolstered by the financial deregulation of the 1980s and high-profile privatisations like British Telecom and British Gas. Today, it is maintained by FTSE Russell, a subsidiary of the London Stock Exchange Group, and is calculated in real time.
The index’s composition is its most defining feature. Because it tracks the largest UK-listed firms, many of which operate globally, its movements often reflect international trade dynamics rather than local conditions. For instance, when sterling devalued on Black Wednesday in 1992, the index constituents benefited significantly as their exports became cheaper. Consequently, analysts often suggest the FTSE 250, which contains fewer international companies, provides a more accurate reflection of the UK economy.
The mechanics of the index are complex, relying on a Chained Paasche Index formula to account for corporate actions and constituent changes. This ensures continuity in the index value despite rebalancing. As of 2026, the index is heavily concentrated, with sectors like Banks, Energy, and Health Care accounting for over half of its total capitalisation. This concentration means that the performance of a few giants, such as AstraZeneca or HSBC, can disproportionately influence the index's direction.
Recent years have seen a shift in the index's landscape, marked by a wave of delistings. In 2024, the market saw its highest number of delistings since the 2008 financial crisis, as companies sought cheaper costs or higher valuations on exchanges like the NYSE. With private equity takeovers further shrinking the pool of available companies, the future composition of the index remains a subject of intense market speculation.
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Sources
- Summary by Intellect · source: FTSE 100 Index
- Also: Wikidata — FTSE 100 Index · CC0
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