Peter Capaldi, Liz May Brice and Paul Copley will all have prominent roles in Torchwood: Children Of Earth, which will be shown over five consecutive nights on BBC One next spring.
Capaldi, best known for The Thick Of It, will play civil servant Mr. Frobisher - a man trying to conceal a terrible secret. The renowned actor recently guest starred in the Doctor Who story 'The Fires Of Pompeii' as Caecilius.
Brice, who played convicted murderer Pat Kerrigan in ITV's Bad Girls, will take on the role of Johnson - a cynical undercover government agent with a mission to expose Torchwood. Copley, best known for recurring roles in The Lakes, This Life and Coronation Street, will play the traumatised figure of Clem.
BBC Wales Head of Drama Julie Gardner hailed their involvement and stated: "Joining our main cast are some fantastic guest artists who will only add to making this unmissable TV."
Series regulars John Barrowman, Eve Myles, Gareth David-Lloyd, Kai Owen and Tom Price will all be returning.
> Click here for our review of Torchwood's second season