Blunt Speaking, Minerva Theatre, Chichester

Blunt by name, but not by nature

On the face of it, the title is awful, with its pun on Anthony Blunt's name and what could be a scoutmaster's advice to young men. But it's also the first of many ironies in Corin Redgrave's entertaining and subtle play. Straight talk is, of course, the last thing we expect from the art historian who, while working for MI5, spied for the KGB. How much, if any, do we get?

Mark Clements' production has a handsome set. An enormous, broken guilt frame looms over Blunt, and a screen within it shows his contemporaries (Edward VIII, Hitler), then pictures by Poussin, Blake, and, suggestively, Caravaggio. There is no mention of Blunt's love life, even though he was living with a much younger man at the time of the play (several days after 14 November, 1979, when he was exposed by Margaret Thatcher as a double agent), and though sex may have been the mainspring of his treachery – he was introduced to Marxism by the gorgeous Guy Burgess.

Redgrave doesn't look at all like Blunt, who was 72 at the time of his unmasking and had the kind of countenance that suggests the upper classes long ago mastered genetic engineering, managing to cross a human with a sheep or a camel. Blunt tells us that, waking up confused in hospital, his mother blinked at him and thought she had received a visit from his third cousin, Queen Mary.

But, aside from gestures that seem too spacious for this calculating and secretive man, his is a wonderful impersonation – reflective, fearful, acidic, furious at both his "betrayal" and the "middle-class morality" that has stripped him of his title. (MI5 had promised Blunt immunity and discretion in exchange for a full disclosure when it discovered the truth; his debriefers gave their word of honour).

Despite Blunt's coldness and self-justification, Redgrave makes us feel some pity for this repressed, bitter man, an enigma even to himself. The best stories are not about spying but about Blunt's pride and embarrassment at his family. A Blunt appears in Henry IV. "He follows the king everywhere, hardly saying anything, just oozing loyalty," until, disguised as the monarch, he is killed in his place. "That's what you got for loyalty in those days." A pause. "Still do."

As a child, Blunt saw little of his mother – whom he "loved, of course" – but he "adored" nanny. That grand passion, though, seemed to mean permitting her to love him, then not giving her a thought when his taste moved on to petty thieves and sailors. There is a moving encounter in which Blunt is taken aback by nanny's worship of him after so many years, knows he ought to care for her, and doesn't.

Another anecdote, brilliantly combining Blunt's snobbishness, weakness, and guilt, begins with his trying to keep his mother, looking so scruffy his doorman takes her for a tramp, out of the sight of a wealthy donor to the Courtauld, of which he was then director. It ends with him flat on his back, the donor's lips pressed to his.

As his ancestor did, Blunt says, "I have done the state some service, and they know it." He recounts the tale (based on a mission Blunt did perform for George VI) of destroying documents and pictures that would have greatly damaged the Royal Family. One thinks, on hearing his indignation, of another literary figure, who asked, "what right have you to butcher me?"

But, characteristically Blunt Speaking ends on notes of sentimental, homosexual-sentimentality and schoolmasterly smugness. Redgrave's fascinating play has told us a great deal about Blunt, but does the title really apply? Or just its initials?

To 10 Aug (01243 781312)