Nearly ten years after its premiere at the National Theatre, Michael Frayn’s Democracy still impresses and moves me as one of the most enthralling plays about modern politics of the past 20 years.

And since the advent of our own Coalition government, the twists and turns, deals and deviations in the Bonn parliament of Willy Brandt, the German chancellor from 1969 to 1974, take on a special resonance and application, without any added emphasis.

But Democracy is a tragedy, too, in the undermining of Brandt’s great project, that of forming a new fatherland of love and justice while “daring more democracy” with the Communist bloc, by treachery within his own camp.

Paul Miller’s production for the Sheffield Crucible – where it opened in March – may not have the sleek, compelling authority of Michael Blakemore’s original staging, but it is lucidly laid out on the Old Vic stage and given an eerie layer of vocal enhancement that makes all the dialogue sound like private speech coming over as public.

At the centre is the story of two remarkable men drawn to each other in a strange friendship, both troubled by anxieties and, in Willy Brandt’s case, depression. Patrick Drury as Brandt is a much colder fish than the character we think we know (and the one we saw in Roger Allam’s original performance), but he does suggest an unshakeable dignity and integrity of purpose.

He is kept going, ironically, by the man who is betraying him, Aidan McArdle’s wonderfully comic and slippery Günther Guillaume, an East German spy who is operating as his personal assistant while feeding information to his permanently onstage Stasi contact, Arno Kretschmann (leather-jacketed Ed Hughes).

The stage is full of other “suits,” all briskly characterised in this game of cat and mouse and push and shove: David Mallinson’s Helmut Schmidt, the ruthlessly ambitious coming man; William Hoyland’s pipe-smoking Herbert Wehner, masking his Machiavellianism in a smiling cloak of bonhomie; and Richard Hope’s Horst Ehmke, the chief of staff whose vetting procedures are so woefully inadequate.

The play has the serpentine quality of a good thriller, especially in the first half, and has much in common, in terms of spirit and argument, with the recent movie of Tinker Tailor Soldier Spy.

There’s only so much chit chat about the economy that you can absorb in one play, but Democracy has the brilliant knack of re-drafting every shimmy and shift in policy and politics as a personal and revelatory statement, a box on the ears or a stab in the heart.