"In play" is day-trader shorthand for the names everyone is watching today: something has happened, volume is pouring in and the price is moving. This screen lists stocks on the London Stock Exchange up or down more than 3% today on at least twice their 21-day average volume, with an average true range above 3% of the price, so there is room to trade. The heaviest relative volume comes first. LSE prices are quoted in pence, and the list skips thinly traded shares.
