What Are Index Funds and How Can You Invest in Them?
Today I thought I would take a closer look at Index Funds. These are among the most straightforward and cost-effective ways to invest in the stock market – especially for long-term savers and beginners.
Instead of trying to pick individual shares, index funds track a market index such as the FTSE 100, giving you broad exposure to many companies at once. This helps spread risk and keeps costs low.
In this article, I’ll explain what index funds are, which market indices they track (with a focus on popular UK and global examples), the pros and cons of index investing, and how you can invest in these funds from the UK.
Table of Contents
What Is an Index Fund?
An index fund is a type of pooled investment that aims to mirror the performance of a specific stock market index such as the FTSE 100 or the S&P 500, rather than trying to beat it via active stock picking.
Because these funds simply follow a set rule (i.e. “invest in all the companies in this index”), they tend to have much lower fees than actively managed funds.
Common Market Indices Tracked by Index Funds
UK Market Indices
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FTSE 100 – Tracks the 100 largest companies on the London Stock Exchange, such as Shell and HSBC.
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FTSE 250 – Covers mid-sized UK companies (not including those in the FTSE100), giving broader UK-specific economic exposure.
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FTSE All-Share – Includes hundreds of UK companies across large, mid and small caps.
International Indices
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S&P 500 (USA) – 500 of the largest US companies by market value.
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FTSE All-World – Broad global coverage of thousands of companies across developed and emerging markets.
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MSCI World – Tracks large and mid-cap companies in developed economies.
Popular UK Index Funds You Can Invest In
Here are some specific examples of index funds and ETFs available to UK investors:
UK-Focused Trackers
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iShares Core FTSE 100 UCITS ETF (LSE: ISF) – Tracks the FTSE 100 index with a low ongoing charge (~0.07%).
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Vanguard FTSE 100 UCITS ETF (VUKE) – Another FTSE 100 tracker, from Vanguard.
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Vanguard FTSE 250 UCITS ETF – Provides exposure to mid-sized UK companies via the FTSE 250 index.
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HSBC FTSE 250 Index Tracker – A low-cost option that tracks the FTSE 250.
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Vanguard FTSE UK All-Share Index Fund – A broader UK fund tracking a wide range of UK shares.
Global and International Trackers
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SPDR S&P 500 UCITS ETF – Tracks the S&P 500 for US market exposure.
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FTSE All-World ETFs / Funds – Provide broad world-wide market exposure including developed and some emerging markets (often available via major brokers under names like FTSE All-World).
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iShares MSCI World ETFs – Track global developed markets outside the UK.
💡 Most of these are available as ETFs you can buy and sell on the London Stock Exchange, and many can be held inside tax-efficient accounts like ISAs and SIPPs.
Pros of Investing in Index Funds
✅ Low Costs
Index funds usually have much lower fees than actively managed funds because there’s no expensive stock-picking involved.
✅ Diversification
A single index fund can give you exposure to hundreds or thousands of companies, spreading risk across many businesses.
✅ Simple and Transparent
The strategy and holdings are easy to understand – you know exactly which index you’re following.
✅ Competitive Long-Term Returns
Over long periods, passive index funds have often matched or beaten actively managed funds, especially after fees.
Cons of Investing in Index Funds
⚠️ You Can’t Beat the Market
Index funds aim to match the performance of their benchmark, not outperform it.
⚠️ No Protection in Downturns
When the market falls, your fund generally will too – there’s no active manager moving your investment into “safer” assets.
⚠️ Concentration Risk
Some indices (e.g. the S&P 500) are heavily weighted toward certain sectors (like tech), so your exposure might be concentrated.
Ways to Invest in Index Funds in the UK
🪙 Through a Stocks & Shares ISA
This is one of the most tax-efficient ways to hold index funds: you won’t pay UK taxes on gains or dividends each year.
🧓 Via a SIPP
Index funds can form the core of a low-cost SIPP (Self Invested Personal Pension) portfolio. Contributions may also receive tax relief.
📈 Through Investment Platforms
Platforms like Hargreaves Lansdown, AJ Bell, Interactive Investor and Trading 212 let you buy and manage index funds directly.
🤖 Robo-Advisers
Services like Nutmeg (recently renamed JP Morgan Personal Investing) or Moneybox automatically build diversified portfolios using index funds based on your risk profile.
Final Thoughts
Index funds are an excellent foundation for long-term investing – especially if you want a low-cost, diversified, hands-off approach. With options covering UK, US and global markets, you can build a portfolio that matches your goals and risk tolerance.
Disclaimer: I am not a qualified financial adviser and nothing in this article should be construed as personal financial advice. It’s important to do your own ‘due diligence’ before investing and speak to a professional financial adviser/planner if in any doubt how best to proceed. All investments carry a risk of loss.