Michael Frayn is a playwright with a name so instantly associated with the supply of entertainment that it appears on theatre billboards in the same size print as the title of the work being performed. At the Old Vic, last year’s hit production of his hilarious behind-the-scenes theatrical farce Noises Off (now completing its run at the Novello Theatre) is succeeded by a revival from Sheffield Theatres of his 2003 ‘political thriller’ Democracy, concerning the fall from power in 1974 of the West German Chancellor Willy Brandt.

Its focus is a spy at the heart of his fragile coalition government — notice any modern resonances? — in the shape of East German ‘sleeper’ agent Günter Guillaume, who is presented in surprisingly sympathetic style by Aidan McArdle. Drafted initially into the Social Democrat leader’s team to liaise with trade unions, he rises to become Brandt’s principal confidant.

That one of his roles turns out to be as a Leperello to his increasingly Don Giovanni-like boss is another reason why Brandt must step down when the agent is eventually unmasked.

In a well-judged, hugely watchable performance, Patrick Drury gives a convincing portrait of a man with a just claim (which Frayn certainly helps to make) to have been prime mover in the process of rapprochement with the Eastern bloc that led in 1989 to the fall of the Berlin Wall.

“Dear friends” — the oft-heard, tenderly delivered start to so many of his political speeches suggests the sincere regard he had for the people of his country. Many felt the same towards him. Away from the spotlight, however, we see some of the problems besetting the private man, including depression and booze.

The double life led by Guillaume is illustrated by the device — daring but effective — of placing on stage for most of the action his Stasi handler Arno (Ed Hughes), from whom orders are taken and to whom reports are made.

Frayn owns in a programme note to his concern at showing us “ten men in suits”, by which he means giving us a play without women. An associated difficulty arises in the job one sometimes has sorting one very similar character from another.

No problem on that score, though, with William Hoyland’s portrait of the machiavellian SPD party chairman Herbert Wehner, or with David Mallinson as the scarcely more likeable Helmut Schmidt. Backstabbing? Both manage it to a fine art.

Until July 28. Tickets: 0844 8717628 (www.oldvictheatre.com).