Perhaps because Guy Burgess and Anthony Blunt were both traitors, both toffs and both gay it has become traditional for the same actor to play them in productions of Alan Bennett’s 1989 double-bill Single Spies. Robert Powell and Nigel Havers did fine work on the two previous occasions I have seen it. In director Jamie Glover’s well-managed revival at the Watermill Theatre acting duties are split between James Clyde as Burgess and David Yelland as Blunt. The evening is the better for it.

The casting serves for once to emphasise the difference between the two men — Burgess so rackety, boozy and indifferent to anyone’s opinion of him; Blunt so patrician, proper and jealous of his position in court as Surveyor of the Queen’s Pictures. The first is glimpsed at a low point in his life in An Englishman Abroad, living in a seedy Moscow flat following his exile from the UK where he successfully persuades visiting actress Coral Browne to measure him up for a Savile Row suit which is later sent out to him by his tailor. Blunt is found, in A Question of Attribution, preparing to expose a fake Titian among The Queen’s collection, even as his own authenticity is under scrutiny — not least, it is suggested, by Her Maj.

In line with tradition this time, Mr Glover has cast the same actor — the excellent Melanie Jessop — as both The Queen and the famously foul-mouthed Coral. That she excels in the first role will be obvious to anyone who has ever tuned into a Christmas Day broadcast — though I doubt our monarch feels quite the fascination shown here for the technicalities of the swimming pools, factories and the like she is called upon to declare open. Ms Jessop’s success at the second will be recognised by all who remember the 1983 TV version of the play in which Ms Browne played herself.

Mr Clyde shifts gear after the interval to give us Blunt’s down-to-earth interrogator, the play’s one strong reminder of the real and dangerous world in which the traitors plied their trade. Mr Yelland offers in the first play a winning portrait of Burgess’s unflappable tailor — in which role he might have pointed out, apropos Blunt’s grey three-piece suit (right), that a gentleman insists on four (not three) buttons at the cuffs and always keeps the last waistcoat button undone.

Until November 6. Box office: 01635 46044 (www.watermill.or.uk)