The Venus and Perrier's Bounty actress has been cast as a trainee nurse, Sam, who gets caught up in an alien invasion with a gang of youths on a South London estate. Nick Frost and Luke Treadaway are among the supporting cast, along with newcomers John Boyega, Alex Esmail, Franz Drameh, Leon Jones and Simon Howard.
Cornish, who has written Tintin for Steven Spielberg and Ant-Man for Edgar Wright, also penned the screenplay for Attack The Block.
One half half of the comedy double-act with Adam Buxton, he first appeared on TV on late-night Channel 4 show The Adam And Joe Show in 1996.
Filming kicked off this week on the action-adventure comedy, which is being backed by Big Talk, Film4, the UK Film Council and Optimum Releasing.