The UK Stock Market: How the LSE, FTSE Indices, and Share Trading Actually Work

How the UK stock market actually works — London Stock Exchange structure, FTSE index mechanics, how shares are priced, and what UK investors need to understand first.

The UK Stock Market Explained

The UK stock market is one of the oldest and most established in the world. For UK investors, understanding how it works — the exchanges, indices, sectors, and mechanics — provides essential context for every investment decision.

This guide explains the UK stock market in plain English: how the London Stock Exchange operates, what the FTSE indices measure, how shares are actually traded, and how investors typically analyse UK companies.

The UK stock market explained (quick summary)

The UK stock market is centred on the London Stock Exchange (LSE), where thousands of companies have their shares listed for public trading. The market is organised into indices — most notably the FTSE 100 (largest 100 companies) and FTSE 250 (next 250) — which track performance across different segments. Shares are traded electronically during market hours, and settlement currently follows a T+1 cycle.

The UK market is often associated with dividends, financials, and energy — a very different composition from the technology-heavy US market.

How the London Stock Exchange works

The London Stock Exchange (LSE) is the primary venue for buying and selling shares of UK-listed companies. It operates two main markets:

Market	Type of company	Regulation	Listing requirements
Main Market	Large, established companies	Heavily regulated by FCA	Strict financial history and governance requirements
AIM (Alternative Investment Market)	Smaller, growing companies	Lighter regulation	Fewer requirements, designed for growth companies

The Main Market includes most FTSE 100 and FTSE 250 companies. AIM hosts over 700 smaller companies, many of which are earlier-stage businesses. AIM shares can be more volatile and less liquid.

Trading hours are typically 8:00am to 4:30pm (London time), Monday to Friday.

UK stock market indices

Indices group companies together to track the performance of different market segments.

Index	Companies	Market cap	Key characteristics
FTSE 100	Largest 100	Large-cap	Global revenue focus, dividend-heavy, sector-concentrated
FTSE 250	Next 250	Mid-cap	More UK-domestic, higher growth potential
FTSE All-Share	~600	Broad	Combines FTSE 100, 250, and SmallCap
FTSE AIM All-Share	700+	Small/micro-cap	Higher risk, earlier-stage companies

The FTSE 100 gets the most attention but represents only a fraction of UK-listed companies. Many investors also track the FTSE 250, which is more closely linked to the UK domestic economy.

For a detailed breakdown of the FTSE 100, see FTSE 100 explained.

How shares are traded

When you buy or sell a share on the LSE, several things happen behind the scenes.

Order types

Order type	How it works
Market order	Executes immediately at the best available price
Limit order	Executes only at your specified price or better
Stop order	Triggers a market order when a price threshold is reached

Settlement

After a trade executes, settlement — the actual transfer of shares and cash — follows on a T+1 basis (one business day after the trade). This means if you sell shares on Monday, the cash settles on Tuesday.

Bid-ask spread

The bid is the highest price a buyer will pay; the ask is the lowest price a seller will accept. The difference is the spread. Larger, more liquid shares (like FTSE 100 companies) typically have tighter spreads than smaller AIM stocks.

Sector composition of the UK market

The UK market has a distinctive sector mix that differs significantly from the US.

Sector	Approximate FTSE 100 weight	Notes
Financials	~20%	Banks, insurers, asset managers
Energy	~13%	Oil, gas, renewables
Consumer staples	~15%	Food, beverages, household goods
Healthcare / Pharma	~12%	Large global pharmaceutical companies
Mining / Materials	~10%	Commodity-driven, cyclical
Technology	~2%	Much smaller than US markets
Other	~28%	Industrials, utilities, telecoms, real estate

This sector composition explains why the UK market often moves differently from the S&P 500 or Nasdaq. Energy and mining prices, currency movements, and global dividend flows often drive UK returns more than tech innovation.

How to analyse UK stocks

Analysing UK shares typically involves understanding a company's financials, valuation, and position within its industry.

Key areas investors examine:

Revenue and profit trends — Are earnings growing, stable, or declining?
Cash flow — Is the business generating real cash, not just accounting profit?
Valuation ratios — How does the current share price compare to earnings, assets, or cash flow?
Dividend history — Is the payout sustainable?
Balance sheet strength — How much debt does the company carry?

A stock analysis tool for UK shares makes this process more accessible by bringing key data together in one view.

Understanding risk and return is also important — even well-analysed investments carry uncertainty.

→ Browse UK shares with the stock screener | → View an example: Shell

Common mistakes

Assuming the FTSE 100 reflects the UK economy — It doesn't. Most FTSE 100 companies earn the majority of their revenue overseas. The FTSE 250 is a better gauge of UK domestic conditions.
Ignoring sector concentration — UK portfolios often end up overweight in financials, energy, and mining without the investor realising it.
Only looking at the headline index level — The FTSE 100 "number" tells you about price movement but not total return. Dividends contribute a significant portion of long-term returns.
Treating all UK companies as the same risk — An AIM micro-cap and a FTSE 100 blue chip are vastly different in terms of liquidity, volatility, and survival probability.
Home bias — UK investors often hold too much in UK equities relative to global markets. The UK is roughly 4% of global market capitalisation.

Guides in this series

Frequently asked questions

What is the London Stock Exchange?

The LSE is the UK's primary stock exchange, where shares of publicly listed companies are bought and sold. It operates the Main Market and AIM.

What is the FTSE 100?

The FTSE 100 is an index of the 100 largest companies listed on the LSE by market capitalisation. It is the UK's most widely quoted stock market benchmark.

How many companies are listed in the UK?

The LSE lists over 2,000 companies across the Main Market and AIM combined.

Can anyone buy shares on the LSE?

Yes. UK residents can buy shares through a stockbroker or investment platform. You'll need an account (ISA, GIA, or SIPP) to hold them.

Why does the UK market behave differently from the US?

Different sector composition (less tech, more energy and financials), different currency (GBP), and different economic drivers create divergent performance patterns.

Is the UK stock market open to international investors?

Yes. Shares listed on the LSE can be bought by investors worldwide, though tax treatment varies by jurisdiction.

Start analysing UK shares

Understanding the UK market is the foundation. Seeing how individual companies perform is the next step.

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This page is for educational purposes only and does not constitute financial advice.