“It seemed the right thing to do at the time.”

This line, uttered during both acts of Alan Bennett’s Single Spies, is not the only thing Guy Burgess and Sir Anthony Blunt had in common.

Both men enjoyed a whisky, both were openly gay and both were members of the Cambridge Five, the infamous spy ring who leaked British secrets to the Soviet Union during and after World War II.

The Rose Theatre’s revival of Bennett’s award-winning double bill opened last week, and runs until October 11.

The play is essentially an examination of traditional English values, and their transience.

It opens with Act One, an Englishman Abroad, with Guy Burgess (Alexander Hanson) inviting Australian actress Coral Browne (Helen Schlesinger) to lunch at his grubby flat in Moscow, where he lives in exile following his outing as a double agent.

The pair make small talk, while Burgess nonchalantly munches garlic, and convinces Browne to order him a new suit from Savile Row when she returns to London.

For a man who betrayed his country, Burgess still has a deep love for the place, even fondly reminiscing about the British class system (“I am English,” he laments, in reference to his status in Moscow).

But while Burgess is happy to pass the time listening to his one and only record (by Jack Buchanan, Browne’s ex-partner), Browne is more interested in talking about the giant elephant in the room – why he betrayed his country.

Hanson and Schlesinger clearly have a ball – Hanson’s top lip quivering throughout with camp, comic timing, Schlesinger the embodiment of an outrageous, seasoned thesp.

It's an enjoyable watch without really catching fire until the final 10 minutes. The reason for that is not the performances, which are excellent, but with the story itself.

Burgess is out, in more ways than one, and has little to lose now, bar his health (he died an alcoholic in 1963).

Little reason is given for his defection, bar that one, definitive line: “It seemed the right thing to do at the time.”

Bennett is more interested in what became of Burgess, and how his decision effected his life afterwards. Burgess was only allowed to return to England until after his death, and the play asks whether his excile, in hindsight, was entirely justified.

When Burgess asks Browne what they say about him back home, Browne replies: "Not very much, these days." Burgess seems genuinely deflated.

It's a poignant moment in an intriguing, and occasionally gripping, piece.

In the second act, A Question of Attribution, the stakes are higher, and for that reason – at least from a dramatic point of view – it is the superior act.

Because unlike Burgess, Sir Anthony Blunt still has everything to lose.

Blunt (Michael Pennington) is the Surveyor of the Queen’s Pictures, an eminent Pouissin scholar - and the subject of a police investigation into his past as a Russian informant.

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Michael Pennington as Sir Anthony Blunt and Alex Blake as Chubb in A Question of Attribution

Bennett neatly frames the story through Blunt's pursuit of the truth behind a disputed Titian painting.

Having admitted his involvement with the Cambridge Five in return for immunity, he is forced to carry out his own investigation while simultaneously giving up information on his former co-conspirators to a dogged interrogator (Alex Blake), who himself has become well-versed in art criticism as a result of his dealings with Blunt.

But it transpires that although Blunt may have immunity from prosecution, his anonymity, in the higher echelons of power, may not be so watertight.

This is brought into play with great comic effect when Blunt meets the Queen (a pitch-perfect Schlesinger again), and the pair discuss the true value of a painting if it is not by the person it is claimed to be.

Every time the monarch refers to the work as a "fraud", Blunt winces uneasily, repeating his mantra that a fake is different to something "that is not what it appears to be".

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Michael Pennington in A Question of Attribution

Pennington’s performance is brilliant, helped by his uncanny ability to seemingly age about 20 years every time he suspects Her Majesty knows more about him than she is letting on.

The second act's set also makes better use of the Rose's space, coming to the fore during the play's denouement.

Single Spies is another piece of accomplished theatre by the Rose, and loyal to Bennett's source material (even the reference to the Bentall Centre was, I'm told, true to the original).

With a week to go before the show closes, it is well worth catching, if only to see a group of accomplished actors having a fine time with the work of one of Britain's greatest living playwrights.