MUMBAI: BBC has announced that the fourth season of Doctor Who has started filming, with Catherine Tate joining the drama series as The Doctor's brand new companion Donna Noble.

The season will kick off in the UK on BBC One next year. In India the show airs on BBC Entertainment which is being carried by Tata Sky.

Tate is reprising her role as Donna, the runaway bride who featured in last year's Doctor Who Christmas special. The start of the new series will see Donna tracking down the Time Lord during an alien emergency in modern-day London.

The couple are destined to experience a series of wonderful adventures throughout the new series including meeting one of Doctor Who's most popular aliens, The Ood, in a brand new episode, Planet Of The Ood.

Donna and The Doctor – David Tennant – will also be travelling through time for an encounter with the legendary murder mystery novelist, Agatha Christie.

Agatha Christie will be played by Jekyll star Fenella Woolgar and The Good Life actress Felicity Kendal will star as Lady Clemency Eddison.

Doctor Who's executive producer and head writer, Russell T Davies says, "Visiting Agatha Christie has been on my wish-list for ages now and, for the Doctor, it's a real meeting of minds! Viewers can expect many more ambitious storylines and a whole host of guest stars in 2008."

Agatha Christie's grandson Mathew Prichard says, "What a brilliant idea that Agatha Christie and Doctor Who should meet! Two characters whose contribution to British entertainment is absolutely unrivalled.

"As far as I know my grandmother, Agatha Christie, never saw Doctor Who, but I am sure she would have been intrigued, excited and above all flattered by all this attention in 2007."

Tate says, "I am delighted to be returning to Doctor Who. I had a blast last Christmas and look forward to travelling again through time and space with that nice man from Gallifrey."

Freema Agyeman who has played Martha Jones, The Doctor's companion throughout the critically acclaimed third series, will return to the show to join The Doctor and Donna mid-series.