The Time Lord's feeling lonely this Christmas – but at least there's a new girl on the scene to perk him up.

Diana Pilkington takes a tour of the famous Doctor Who set and meets new sidekick Jenna-Louise Coleman.

There's nothing like being on the Doctor Who Christmas special set to get you in a Yuletide mood.

It's August when I visit the Cardiff studio, but a blanket of snow covers the narrow streets of Victorian London and, round a corner, I glimpse the Tardis surrounded by pine trees.

The show's festive episode is always one of the biggest events of the TV calendar, but

there's an extra reason to watch this year. It's the first time fans will see Jenna-Louise Coleman as the Doctor's new sidekick, Clara.

The actress made a surprise appearance in September in the role of Oswin, who was in fact a Dalek, but she insists Clara is another entity.

'I'm not Oswin. I'm a different person,' says Coleman, fresh from wardrobe in a corseted burgundy gown. 'The connection is that it's me playing them both, but this is the mystery. This is where the series goes...' She tails off, at pains not to reveal too much.

As usual, the episode, titled The Snowmen, is shrouded in secrecy. What we do know is that it features the villainous Dr Simeon, played by Richard E Grant, who controls an army of snowmen with sharp icicles for teeth.

The Doctor (Matt Smith) first meets Clara as a barmaid, but viewers later discover she is a governess to the children of Captain Latimer (Tom Ward).

The episode also sees the Time Lord joined by familiar characters Silurian Madame Vastra,

her human friend Jenny and the friendly Sontaran Strax.

Downhearted and reclusive after the departure of Amy (Karen Gillan) and Rory (Arthur Darvill), the Doctor is initially reluctant to engage with the problems of the

universe, but Clara wants his help and won't back down until she gets it.

Coleman says: 'She's feisty and curious. She's up for adventure and knows what she wants

and is very witty. She's not intimidated by the Doctor – she finds him amazing and ridiculous

in equal measures.'

Faced with the inevitable question of a possible romance, she says: 'There's definitely a flirtation between them both and they're definitely drawn to each other.'

For any actress, taking on the coveted role of the Time Lord's sidekick is a huge deal. As well as the media interest and the legions of devoted fans, there's the need to keep lots of details under wraps.

'I wasn't allowed to say what I was auditioning for, I had to call it Men On Waves. And we had

different character names – Jasmine was one of them,' says the actress, who is best known, coincidentally, for playing Emmerdale's Jasmine Thomas.

'We had three auditions all at the basement of the BBC, and when I got told I got the part I

could only tell my mum – because that's what Karen did.'

Laughing, she adds: 'I think she thought I was winding her up.'

The 26-year-old, who's been on a self-imposed 'Google ban' since her casting was announced, admits the past few months have 'been kind of crazy'.

'For the last two years I've mainly been doing period dramas and now I've been thrown into this where there's CGI and it's very technical but also very fun and adventurous and it's OK to run down a corridor shouting.

'You can basically be as silly and ridiculous as you like and some of the scripts are so emotional and heartfelt as well. It really does give you everything.'

The hardest part, she says, is coping with all the action-packed scenes.

'I get so carried away with the adventure that I end up being really clumsy and headbutting the camera in every single episode!'

The intense workload means she's had no time to process the enormity of the role, but has had support from those well versed in the Doctor Who machine.

'Karen's been great. She's texted me and given me some advice on where to eat in Cardiff and that kind of thing. And Matt has always got an ear out for me.'

Doctor Who is on BBC1 on Christmas Day