The lead writer on the BBC's Doctor Who and Sherlock has lamented the impending departure of Matt Smith as The Doctor from the world's longest running sci-fi series.

Speaking on a panel at the Doctor Who 50th Anniversary Celebration event in London at the ExCel centre, Moffat said that he was not only losing his close friend but the TV show has lost "one of the best actors I have ever worked with."

"I'll be losing a friend and the most timelessly inventive, hardworking and best actor I have ever worked with," said Moffat, while sat next to Smith and the latest companion Jenna Coleman.

Following the statement, Moffat recalled the time when Smith first became The Doctor and Moffat had more of a stake in the TV show.

"I remember in the first year, we would go to the US where no one knew who he was and he had to ask whether he should go out and sign autographs," said Moffat.

"In fact, no one knew who we were and everyone looked at us like we were idiots for thinking we could make Doctor Who huge.

"Critics may say that Doctor Who isn't what it used to be but any previous series hasn't even come close to the success we have now - and that is largely down to Matt."

The show has over 77 million fans worldwide, and thousands gathered in London to catch a glimpse of their favourite Doctors in person, as well as grab a photo or a signed autograph from the Timelords.

In the audience, some travelled from Australia, US and even Brazil for the weekend event in London.