It’s taken more than 60 years for a theatrical version of John le Carré’s revolutionary spy novel to find its way on to the stage, and judging by this pioneering presentation it’s easy to see why: there’s so much for the actors to convey, and even more for the audience to take in.

Written in the midst of the Cold War in 1963 (a movie version starring Richard Burton followed two years later) – the twisting thriller focuses on MI5’s Berlin station head Alec Leamas. Already broken by a life of deceit and mourning the death of an agent he was handling, he’s sent on a final mission to frame East German operative Hans-Dieter Mundt by making the Soviets think he’s a Western double agent. Keeping up so far? Making this happen is a complicated business, and the waters are muddied further when Leamas meets, and falls for, an idealistic, left-wing librarian while back in London. The plot thickens, the twists turn and the turns twist.

I’ll give away no more plot than that, even though it might help readers planning to attend, especially those unfamiliar with the source material, as the story takes some keeping up with. Beyond some early exposition you need to have spy levels of attention (including to detail) to stay in touch, not least because some of what’s happening is genuine and some of it Leamas’s thoughts, nightmares and false memories, while the non-stop dialogue is as dense as it is incredibly tense.

The latter is very much the prevailing vibe of David Eldridge’s dark (mostly in the shadow of the Berlin Wall) and efficient adaptation, and no doubt designed to reflect the pressure of staying in character and the toll that constant pretence, moral compromise and deception exacts on the individuals involved.

That arguably includes the terrific ensemble cast, which is led by TV star Ralf Little who gives a hugely impressive performance as Leamas. It’s some leap for the Royle Family’s Lurky to be playing a role made famous by acting royalty, but he acquits himself admirably – not least as he has more lines than a Berlin telephone exchange and is on stage virtually the entire time.

Mercifully that’s only 135 minutes (including interval), because as much as The Spy Who Came In From The Cold is a thrillingly riveting piece of theatre, there are times when the intensity borders on unbearable. By the end I was happy to get out in the warm.

Four stars

Reviewed by Steve Adams at The Alexandra, Birmingham, on Tuesday 30 June. The Spy Who Came In From The Cold continues to show at the venue until Saturday 4 July.