ETFs Explained: A UK Investor's Guide

An ETF is a pooled investment fund whose units are bought and sold on a stock exchange throughout the trading day, much like shares. Each unit represents a slice of a portfolio of underlying assets chosen by the fund manager, usually to track a specific index. If you buy a FTSE 100 ETF, your money is invested across the 100 largest companies listed on the London Stock Exchange in proportions set by the index.

Most ETFs are passive, meaning they aim to match the performance of their chosen index rather than beat it. A smaller but growing number are actively managed, aiming to outperform a benchmark through security selection. Both structures share the defining feature: they trade on exchange rather than being bought and sold once a day at a single price like a traditional open-ended fund.

UK investors typically choose between three main pooled investment structures:

• Traditional open-ended funds (OEICs and unit trusts): priced and traded once a day at the fund's net asset value. Simple to understand, and often used for regular savings.
• Investment trusts: closed-ended companies whose shares trade on the stock exchange. Their price can move to a premium or discount relative to the net asset value of the underlying portfolio.
• ETFs: open-ended in effect (new units can be created or redeemed by large market-makers) but traded on exchange throughout the day. The market price typically stays very close to net asset value thanks to an arbitrage mechanism.

The practical differences matter less than you might think for a long-term investor choosing a broad index tracker. Costs, tax treatment and the quality of the underlying index are usually more important than the wrapper.

Three figures tend to matter most:

• Ongoing charges figure (OCF): the annual cost of running the ETF, typically between 0.05% and 0.50% for broad index ETFs and higher for specialist or active ones.
• Tracking error / tracking difference: how closely the ETF has tracked its benchmark net of costs. Small, consistent tracking is usually a good sign.
• Bid-offer spread: the gap between buying and selling price, which is a real cost each time you trade. Broad, liquid ETFs tend to have tight spreads.

Platform fees and dealing commissions on top of the ETF's own costs also matter, particularly for investors making regular small contributions.

Most UK-listed ETFs are eligible to be held within a Stocks and Shares ISA or a self-invested personal pension. Held inside these wrappers, growth and income are free of UK income tax, dividend tax and capital gains tax.

Held in a general investment account, gains above the £3,000 annual exempt amount for 2025/26 are subject to CGT at 18% (basic rate) or 24% (higher or additional rate), and dividends above the £500 dividend allowance are taxed at the relevant dividend rates. For many investors it is more tax-efficient to hold ETFs inside an ISA or pension wrapper where possible.

Many ETFs popular with UK investors are domiciled in Ireland or Luxembourg for structural reasons. HMRC distinguishes between "reporting" and "non-reporting" offshore funds. Gains from non-reporting funds are taxed as income rather than capital gains, which can significantly increase the tax charge for higher earners.

Most major ETFs aimed at UK investors hold reporting fund status, but it is worth checking the fact sheet or KID (Key Information Document) before investing, particularly outside an ISA or pension.

ETFs share the risks of their underlying investments: equity ETFs fall when stock markets fall, bond ETFs are sensitive to interest rates, and sector or thematic ETFs can be more volatile than broad index ETFs. Two additional points are worth noting:

• Synthetic ETFs use derivatives to replicate the index rather than physically holding the underlying assets, introducing counterparty risk with the swap provider.
• Concentration risk can arise in seemingly "diverse" ETFs where a small number of large companies dominate the index weighting.

As with any investment, you may get back less than you invest. Longer time horizons generally give markets more opportunity to recover from downturns, but there are no guarantees.