Felicity Kendal will guest star in the next series of Doctor Who, while her former Good Life co-star Richard Briers takes a turn in Torchwood, the BBC has announced.

Kendal will play Lady Clemency Eddison in a story that also features Jekyll actress Fenella Woolgar as murder mystery writer Agatha Christie. Briers will play a "90-year-old man rehearsing for the end" in Torchwood.

The BBC have also released the first new image of the Doctor (David Tennant) and Donna (Catherine Tate) since their last pairing in the 2006 Doctor Who Christmas special (see right).

Donna will join the Doctor as a full-time companion in series four, but Freema Agyeman will also return as Martha Jones after a brief stint in Torchwood.

Head writer Russell T Davies promises "a whole host of guest stars" for the new series of Doctor Who, including Kylie Minogue, Geoffrey Palmer and Blackadder and Notting Hill actor Tim McInnerny.

Richard Briers and Felicity Kendal are most famous for their roles as the self sufficient couple Tom and Barbara Good in the 70s sitcom The Good Life. Briers also appeared in the 1987 Doctor Who story Paradise Towers.

Geoffrey Palmer also has numerous sitcom credits to his name, and previously appeared in the 1970s Doctor Who stories The Mutants and Doctor Who and the Silurians. On both occasions, he met with a grisly end.

Click here for details on the forthcoming official Torchwood magazine.