Image caption Michelle Gomez (L) returned as Missy for the opening episode

Viewers in their millions deserted Doctor Who as it returned to BBC One on Saturday, overnight figures suggest.

An average 4.6m watched Peter Capaldi back for his second series playing the Time Lord, compared with 6.8m for his full debut last year.

It was roundly beaten by ITV's X Factor, which had 7 million viewers (7.3 million including ITV+1).

But reviewers were enthusiastic about the Doctor's return, with the Radio Times giving it five stars.

"We're now in the ninth series in 11 years since Doctor Who's revival, and it shows no sign of fatigue. The first episode rattles along with barely a bum note," wrote Patrick Mulkern in his review.

The Mirror said Michelle Gomez as Missy "steals the episode as the demented Time Lady who kills for fun and prances around in the face of greater evil".

Image caption Jenna Coleman is leaving to star in an ITV series about Queen Victoria

And Catherine Gee in The Telegraph described the opening episodes as "packed full of jaw-droppers, one whopper of a cliffhanger and nerdy nods that date back to the time of Tom Baker."

Doctor Who was the most watched BBC programme of the evening, and ratings will rise once figures for catch-up and iPlayer requests are consolidated.

Jenna Coleman, who plays the Doctor's assistant Clara Oswald, revealed this week that she would be leaving the show, having joined in 2012 when Matt Smith was serving as the Time Lord.

Speaking about her departure, she said: "It's been in the works for a very long time.

"[Writer] Steven [Moffat] and I sat down a year and a half ago and tried to work out the best place to do it and tell a really good story.

"We're not going to give any details but it will happen at some point this season... We worked out a really good story arc out so hopefully people will love it."