The Harry Potter star will appear in an episode devoted to Scottish independence, although his exact role has not yet been confirmed. The show is being brought back by the Gold channel for six 40-minute episodes early next year, written by the original team of Jonathan Lynn and Sir Antony Jay.
David Haig – who played the Prime Minister in the recent stage show based on the sitcom – will be reviving the role of Jim Hacker for television. Other stars from the theatre show will also appear in the TV version, with Henry Goodman reviving his role as civil servant Sir Humphry Appleby, while Chris Larkin will play his opposite number Principal Private Secretary Bernard Woolley.
UKTV's chief executive Darren Childs said the new episodes would chime with real-life events.
He said: "The stories are topical and up to date. There are episodes about coalition, the euro crisis and Scottish devolution. And Robbie Coltrane has agreed to play a very key part in that episode, which is exciting."