Actor David Tennant today hinted Billie Piper could be the next Doctor.

Last week, Tennant announced that he will no longer be playing The Doctor in the BBC's long-running science-fiction programme Doctor Who.

And when asked on BBC Breakfast today if his one-time assistant could step up into the role, he said: "Why not?"

He said: "It's one of those parts that any actor could bring something valid to, because it can be anything and it's a sort of blank canvas everytime.

"The fact is that the difference is a virtue with each Doctor, it's not like you're casting Tarzan where you've got to have somebody who looks good in a loin cloth, it can be anything."

Tennant, who is now on stage as the eponymous hero in Hamlet with the Royal Shakespeare Company at Stratford-upon-Avon, said leaving the series had been a difficult decision.

He said: "Sometimes you've got to take a deep breath and make a decision otherwise I could literally be there when I'm 86 with people thinking 'Is he never going?'

"Who knows what might happen in the future and it is one of those parts that sticks with you... the door isn't closed forever, but in a day to day way I'll be handing over the mantle to somebody else."