Performing a live theatre show is complex enough.

Performing it down the aisle of a moving train carriage, virtually under the nose of audience members, is another proposition altogether.

But that is exactly what the cast and creators of the enchanting Polar Express train ride are tasked with - and relish - throughout the course of the festive season.

Hosted and run by the Mid-Norfolk Railway, the first Polar Express performance is, for many, a sign that Christmas has begun.

Until it was cruelly cut short by the spread of coronavirus, this year's sell-out run was once again enjoyed by thousands of delighted families.

Just how, though, is this uniquely immersive experience put together?

Much of that responsibility falls to Paul Goldsmith, theatrical director.

Mr Goldsmith started out as a performer, before taking the reins as the creator-in-chief in 2019.

As one half of theatre-devising Twisted Reality Productions with his partner, Katherine Vince, he is no stranger to directing and creating shows.

"I performed in 2018 and got a lot of good feedback for the work that I was doing," explained Mr Goldsmith.

"In 2019 they turned round and said 'we want you directing it'."

He added: "During the first year of the Polar Express, it was a case of 'let's give it a go'," he said.

"They soon realised how big it had the potential to be, and here we are four years later.

"Even this year, in the middle of a pandemic, we had an audience of 31,000."

With Miss Vince as choreographer and Mr Goldsmith as director, the Polar Express has gone from strength to strength.

The pair still perform in the show, and Mr Goldsmith admits having that first-year experience solely as an actor gave him the grounding to succeed.

"Doing it as a performer in 2018 really helped because it is so different to any other theatre show," said the 44-year-old.

"We have a stage, set and production team, but the railway throws everything up in the air. It is a real clash of worlds.

"I felt prepared because I understood how the railway team operates and knew it would not be easy.

"You have to be prepared to be unprepared because it is a live train with a constantly changing environment. Then of course there is risk of the trains going wrong."

This year, the Polar Express cast was 38-strong - whittled down from a pool of 2,000 performers from across the UK who auditioned.

There is an emphasis on getting as many local people involved as possible.

Mr Goldsmith said: "Part of our process is getting the very best performers on board, but also decent, kind people because they are going to be together every day for a long and heavy run."

The problem with Covid, however, has been having enough cast members to keep the show going - a challenge that ultimately proved impossible to conquer.

"We created a system of casting where people were able to take on a role should someone not be able to come in," he added.

"With the threat of the new variant, all the team was lateral flow testing. I would breathe a sigh of relief for every one that came in negative."

Perhaps the biggest challenge for Miss Vince and Mr Goldsmith from a creative perspective is ensuring the show does not go stale.

"The show changes a lot from year to year, and part of our remit is to keep developing it." said the latter.

"One of the things that was really important to me was to have full, choreographed dances. After all, we are a theatre show, and this year there were even more.

"Live singing opens the show this year, which is also new.

"There are restrictions because it is licensed. There are certain things that have to happen in keeping with Warner Bros - like 20 minutes of Santa being involved.

"It's difficult because you have to be careful you don't change it too much. We get audience members come back every year who want some things to be the same."

For the Polar Express to continue, Warner Bros must be happy with what Mr Goldsmith and the Mid-Norfolk Railway are producing.

The evidence so far suggests they can do little wrong.

"We'll be going for at least another four years and hopefully beyond that," added Mr Goldsmith.

"So long as audiences keep coming and enjoying it, we will keep doing it."