LSE and AIM Stock Screener: What Breaks on UK Shares

There are around 1,800 companies listed in London across the Main Market and AIM, and most of the tools people use to sift them were built somewhere else. They were designed for the Nasdaq and the NYSE, and UK shares are an afterthought bolted on later. The result is a screener that looks like it is working, returns a tidy list of names, and is quietly wrong.

This guide is about the failure modes specific to the London market: what breaks, why it breaks, and how to screen around it. If you want the general mechanics first, our guide to how to screen stocks covers the step-by-step process. What follows assumes you already know what a filter is and want to know why yours is returning nonsense on a mid-cap in Aberdeen.

Why most stock screeners fail UK investors

Four things go wrong, and only one of them is obvious.

Pence versus pounds. The LSE quotes most shares in pence (GBX), not pounds. A screener that assumes decimal-pound pricing reads a share trading at 245p as £245, which silently corrupts every price-based ratio it calculates. The P/E comes back a hundred times too high, the yield a hundred times too low, and nothing on screen tells you it happened. If a UK stock's valuation looks bizarre on a US-built platform, this is almost always the reason.

Coverage gaps below the FTSE 350. The FTSE 100 and FTSE 250 are well covered everywhere. Below that, in the small caps and AIM companies where mispricing is far more common, coverage thins dramatically. If your screener only knows 400 UK companies, you are screening the most efficiently priced end of the market and ignoring the part where a private investor has any edge at all.

Dual listings and ADRs. Shell, BP, AstraZeneca and others trade in several places. Screeners that do not deduplicate will show you the same business two or three times, and the fundamentals attached to the ADR line are frequently stale. You end up comparing a company with itself and calling it a shortlist.

Accounting standard mismatch. UK companies report under IFRS. A screener applying US GAAP-shaped metrics without adjustment will misprice lease liabilities and R&D treatment in particular. The numbers will look precise to two decimal places. They will not be correct.

The practical consequence is unglamorous but worth saying plainly: if you are screening UK shares, use something built for UK shares. That is a low bar, and a surprising number of platforms fail to clear it.

Score first, filter second

Most people open a screener, see sixty available filters, and start layering conditions until the results list is empty. Then they loosen a filter at random until something reappears. That is not screening. That is fishing.

Starting from a composite score and filtering within it is faster. Openbook condenses financial metrics into factor scores and then into two headline ratings on a 0 to 100 scale: a Reward score for how attractive the fundamentals and valuation look against sector peers, and a Risk score for how much downside the balance sheet, volatility and earnings stability imply.

Because every company is scored on the same basis, you can rank the whole universe in one click and apply two or three filters on top, rather than spending fifteen minutes on filter archaeology. The methodology sets out exactly how the drivers are calculated, which matters when you are deciding whether to trust a number you did not compute yourself.

Four screens you can build in under two minutes

Concrete recipes. Adjust the thresholds to taste, and treat them as starting points rather than gospel.

The contrarian value screen

For unloved businesses that are still fundamentally sound.

Value score: above 70
Quality score: above 50
Net debt / EBITDA: below 2.5x
Market cap: above £250m, as a liquidity floor
Sort by Reward score, descending

The quality and leverage filters do the essential work. Cheap-and-deteriorating is a value trap; cheap-and-stable is a value opportunity. Without those two conditions you will simply surface the market's genuine disasters, of which London has a steady supply.

The quality compounder screen

Businesses that reinvest at high rates of return and grind higher over years.

Return on equity: above 15%
Operating margin: above 12%
Revenue growth, three year: above 8%
Risk score: below 40
Sort by Growth score, descending

Expect this screen to return expensive companies. That is the point. You are looking for durability and accepting that you will pay for it. Whether the growth rate justifies the multiple is a valuation question, not a screening one.

The dividend income screen

For the income portion of an ISA, where the real danger is chasing a yield straight into a cut.

Dividend yield: between 3.5% and 8%, where the upper bound is a filter and not an oversight
Payout ratio: below 75%
Free cash flow: positive for three consecutive years
Balance sheet strength: above average

A double-digit yield on a UK share is usually the market pricing in a cut rather than offering you a gift. Capping the upper bound removes most of them before they waste your afternoon.

The momentum screen

For shorter timeframes, where you are acting on relative strength.

Momentum score: above 80
Price above both the 50-day and 200-day moving averages
Average daily volume: above 500,000 shares
Market cap: above £100m

The volume filter is non-negotiable on the UK market, and doubly so on AIM, which is full of names carrying spreads wide enough to eat a week's gain on entry. If you cannot exit a position inside a single day's normal volume, it does not belong on a momentum shortlist no matter how good the chart looks.

How Openbook screens the UK market

The screener covers the LSE and AIM alongside international markets, with the pricing conventions handled properly, so a 245p share is treated as 245p. The same factor framework is applied to every company, which means the score you see on the screener is the identical score you see on the stock page. Nothing switches frameworks between the two.

From a shortlist, the sequence that works is to read the score drivers rather than the score, check the risk rating for the reason behind it, compare the survivors side by side, and only then go deep on the two or three names that are left. A brilliant idea that takes your financials weighting to 45% is not a brilliant idea, which is what the portfolio tracker is for.

If you want the wider landscape first, our stock analysis guide covers what to do with a company once the screener has handed it to you.

The bottom line

The point of screening the UK market is not to find the answer. It is to eliminate the seventeen hundred companies that were never going to be the answer, so your limited research time goes somewhere useful. Pick three or four filters that reflect what you actually believe, apply them consistently, and handle the pence.

Start screening UK shares free

Frequently asked

Common questions

Why do UK share prices look wrong in some stock screeners?

Because the LSE quotes most shares in pence rather than pounds, and screeners built for US markets often assume decimal-pound pricing. A share trading at 245p gets read as £245, and every price-derived ratio inherits the error, so P/E ratios come back roughly a hundred times too high and yields a hundred times too low. The screener will not warn you. If a UK company's valuation looks absurd on a US platform, check the currency convention before you draw any conclusion from it.

Can you screen AIM stocks?

Yes, though most mainstream screeners cover AIM poorly or not at all, so check coverage before you build a workflow around a tool. When you do screen AIM, always include an average-volume filter. Illiquidity is the dominant risk on that market and no fundamental filter will warn you about a spread wide enough to wipe out your first month of gains. A company can pass every quality test you set and still be effectively untradeable in size.

Why does the same UK company appear more than once in a screener?

Because large UK companies such as Shell, BP and AstraZeneca are listed in more than one venue, and screeners that do not deduplicate treat each line as a separate company. The fundamentals attached to a secondary or ADR line are often stale, so the duplicate is not merely redundant, it is frequently wrong. Screen on the primary London listing and discard the rest.

Do FTSE 100 and AIM shares need different screens?

They need different guardrails rather than different logic. The FTSE 100 is liquid, well covered and efficiently priced, so a screen there is mostly about valuation and quality. On AIM, liquidity and survivability come first, which means a volume floor and a hard look at cash burn before any valuation filter is worth applying. Running an unmodified FTSE screen across AIM is how people end up holding illiquid shells.

How often should I run a UK stock screen?

Monthly is sufficient for fundamental screening, because company financials only update at half-year and full-year results, and UK reporting is less frequent than the US quarterly cycle. Momentum and technical screens should be run weekly at minimum. The interesting signal is usually a company that has just entered the shortlist rather than one that has been sitting on it for a year.