Dame Berwick's train of thought for one-off Theatre Royal pantomime at National Railway Museum

The Theatre Royal management had talked confidently of re-opening the theatre in time for the 2015-2016 pantomime after its £4.1 million refurbishment. However, as early as May 22, the announcement was made that Berwick, Dick and the meerkat would move for a one-off panto in the Signal Box Theatre as part of the Theatre Royal's residency at the National Railway Museum, following in the train tracks of this summer's In Fog And Falling Snow and The Railway Children.

This has given Britain's longest-serving dame – the show's writer and director – plenty of time to re-think the pantomime for a traverse setting, with the 1,000-capacity audience seated in rows of ten either side of a track, on which Mark Walters' set will be transported on and off stage on wheels.

The pantomime devotees will be closer to the action than ever before, and Berwick can sense their expectations of a unique experience rising by the day. "I started writing with the Theatre Royal in mind, and then came the change, and then I realised the nightmare of having to make it work in the new space, which we still won't know till the opening night," he says, with even more caution than usually accompanies 69-year-old Berwick's pre-show nerves.

"Nightmare" is a strong word, but it gives an insight into the scale of the challenge he is facing: to baldly go where no dame has gone before. No flying entry; no "Behind you"; no villain's side for the baddie's entry, as writ in panto lore: convention must be turned on its head.

"What I've done is do my best with this limited stage area, because no-one has ever attempted to produce a pantomime on a traverse stage, but the people of York are all getting very excited about it," says Berwick, who will be playing dame Paloma Polony.

"No-one's ever tried it before but I feel very calm about doing it, thought it was a nightmare [that word again!] to write it. I finished the script at four in the morning on the Thursday before we did the read-through, and I really didn't know when I finished it, how it might work. I've done my best but I'm not a gifted writer, and the difficulty is that I wanted slapstick but the audience will be virtually on top of us.

"It's a 1,000-seat tent; I won't be able to fly; I can't lean on a proscenium arch wall; we can't throw water; every entrance has to be completely choreographed when normally in panto you try to keep it raw. So what we have to do is use our imagination a little more; we have to do that and, to be fair, the audience will have to do that too."

Dame Berwick Kaler at the National Railway Museum, York. Picture: Anthony Robling

Amid the dame's air of uncertainty, he is nevertheless excited. "We'll have the rail track that has worked so well in In Fog And Falling Snow and The Railway Children," says Berwick, who had to withdraw from his role as the Old Gentleman in E Nesbit's story through a now healed injury he called a "fractured earlobe".

"Especially for anyone who hasn't seen The Railway Children, can you imagine the excitement as a child, walking through the National Railway Museum, seeing those wonderful trains, and then seeing the pantomime in the Signal Box Theatre?"

Berwick will make great play of the incongruities of the traverse setting. "If you're on one side, David Leonard's baddie will be entering stage left; if you're on the other, he's entering stage right, which he shouldn't. So for half the audience it's right; for half it's wrong, so every line where possible will reflect that," he says.

"Normally at the Theatre Royal I can only talk directly to the front row of the stalls, but this time I could do the whole show on my own talking to the audience as they're so close. No-one is safe."

The now obligatory pantomime film will remain, and despite the presence of a multitude of trains at the NRM, Dick Whittington will still feature a ship as its most significant form of transport. "It's a tradition of this show, and we'll keep it," says Berwick.

"But you will see things in this one-off pantomime that you won't see in a proscenium-arch theatre, though I've tried to keep all the traditional elements too."

Apparently, paleontology will feature in the storyline, and so will a Lord Mayor with a very dull chain of office. Who could he possibly be referring to?

York Theatre Royal's pantomime, Dick Whittington (And His Meerkat), will be stationed at the Signal Box Theatre, National Railway Museum, York, from December 10 to January 24 2016. Box office: 01904 623568, at yorktheatreroyal.co.uk or in person from the De Grey Rooms box office.