Look Who's having a squabble already ... Doctor and new assistant can't agree on their relationship

They may be set to share a kiss this Christmas but off-screen Doctor Who stars Matt Smith and Jenna-Louise Coleman cannot agree on how to describe their relationship.

Coleman, 26, becomes the Time Lord’s new assistant Clara in this year’s Christmas special, which sees Victorian London under threat from killer snowmen led by Richard E Grant’s evil Doctor Simeon.

Smith, 30, said: “This [companion] relationship… it’s something that constantly evolves. I liken it to an arranged marriage, not that I know what an arranged marriage is like. It’s like, ‘You’re married, have chemistry’.”

But Coleman, known for her four years in Emmerdale, disagreed, instead likening it to a “blind date”.

She added: “I felt like I was on a blind date for a while. It’s like putting two people together — ‘I know someone you’ll like and really get on with… now go on and save the world’.”

Speaking at a screening of the episode at BBC Television Centre in Shepherd’s Bush, Smith countered: “But that doesn’t make sense — our families would have already met and all that.” Humorous squabbles aside, Coleman described the Christmas show as “a bit of a love story” but with a “quite dark” edge. The pair share a steamy kiss in the episode. Smith said: “It’s a hard life. I’m great friends with Richard [Jenna Louise’s partner]. I think in the episode it’s quite a fun bit, it’s nice to see the Doctor on the back foot.

“It can change every week, that’s the beauty of it. One week it’s a love story, one week it’s an action adventure.” Next year is the 50th anniversary of the show and although series supremo Steven Moffat remained tight-lipped about the BBC’s plans, he admitted they were “immense”.

He said: “They are considerable and they will be full of tremendous surprises… I promise you, we’re going to take over television.”

Doctor Who: The Snowmen is on BBC1 at 5.15pm on Christmas Day