Tennant revealed he'd be battling foes old and new in this series, including the Cybermen and a race of cat-nun women, with guest stars including Peter Kay, Pauline Collins and Tony Head.

But he said the strangest of all was starring with Elisabeth Sladen, who played one of the Doctor's companions in the 1970s.

"It's a bit surreal," Tennant confessed. "When I was a kid she was on the TV playing Sarah Jane Smith. When she's suddenly calling me Doctor, it's a bit of an out of body experience."

He was delighted with the reception the cast and crew had received on location in Wales.

"It's such a joy to be filming here - everybody here has been so enthusiastic and so indulgent of us that we have a really lovely time.

"So I'd like to thank the people of Cardiff for putting up with us blocking their roads and asking them to go round the long way while we film scenes!"

Billie Piper also enjoyed filming what turned out to be her final series before leaving the show. In the first episode her body was taken over by Cassandra, the highly-stretched character played by Zoe Wanamaker last year.

Piper added that her own character Rose had toughened up this time to ensure that she doesn't lose another Doctor.

"She's a lot more possessive and slightly more uptight because she thinks at any given moment he could be taken away from her.

"The idea of losing the man she loves is really shocking and sad and she doesn't want it to happen again," she added.

"So she's a bit feistier this time around and very jealous which I love playing - it's so much fun."