"Summer 1954". Oxford Playhouse

If you walk along the same stretch of riverbank every day for six months, then you might be lucky enough to catch the magnificent sight of an otter once or twice. In the same way, if you go to the theatre four times a week for a year, then you'll be rewarded with very occasional evenings of pure magic. Summer 1954, a pairing of two one-act plays by Terence Rattigan, is one of those special nights.

"Terence Rattigan"... The name itself sounds so English, fustian and antiquated; the name of a purveyor of middling bedroom farces, perhaps, or sub-Agatha-Christie murder mysteries. Nothing could be further from the truth.

Rattigan may have been less explosive than some of his wild-child contemporaries like John Osborne and his wife-beating angry young men. He didn't mess with the supernatural like J. B. Priestly. He wasn't the darling of the West End like Noel Coward. But still waters run deep. Rattigan, in his quiet, unassuming way, spoke about the everyday realities of human pain: regret, shame, petty envies and fading love, and his plays seem to echo louder as the decades pass.

This production is an oddity in several ways. The first play, Table Number Seven, is normally performed along with Table By The Window (both of them taking place in the same Bournemouth hotel). But here it is instead paired with The Browning Version. It's a master stroke by Theatre Royal Bath and Living Theatre Productions. Not only have they picked two outstanding pieces of drama, but juxtaposing them intensifies the polite brutality, the heartlessness with an insultingly thin veneer of English etiquette, that runs through each play like bacteria through blue cheese.

In the case of Table Number Seven, something truly rare and special is on display. Rattigan's original version openly told the story of a gay man, Major Pollock, who is outed by the local paper and then ostracised by the other guests at the private hotel where he lives. But, in a case of real life mimicking art, Rattigan, who struggled with his own homosexuality, could not mount the play as written because of the Lord Chamberlain's censorship rules. Instead he buried his gay subtext by having his retired officer accost young women at the local cinema. This was infinitely more acceptable to the audiences of 1954. (How times change.)

Rattigan's unperformed script lay as concealed as his own sexuality in an archive for forty years. It was rediscovered in the 1990s, and now we can see it as the playwright originally intended.

The effect is devastating. Not only does the horrified prejudice of the hotel guests provoke a kind of generational shame in the audience, but the one young woman who stands by Major Pollock presents as sensitively queer-coded herself. The dignity, determination and (ultimately) faltering acceptance that ensues is the dramatic equivalent of a Beethoven symphony.

At the heart of the play are two astonishingly charismatic performances. Nathaniel Parker, as the Major, combines politeness and guilt to heart-rending effect. And Siân Phillips, as the monstrous Mrs Railton-Bell, is simply divine. At 92, Dame Siân is still on tour. She is eternal. With a supremely deadpan delivery she finds comedy and horror in every line. It's an acting masterclass. I actually don't understand how she does it. Siân Phillips was playing Derek Jacobi's grandmother Livia in I, Claudius back in 1976, when I was twelve. Now I'm sixty, and she looks exactly the same. How is this possible?

Some of the play's most prescient lines, though, are delivered by the hotel manager Mrs Cooper (played with enveloping humanity by Lolita Chakrabarti). "The word normal is meaningless", she says, and it reaches out to an entire generation.

Under James Dacre's inspired direction, both plays make subtle but telling use of a revolving set. As it rotates, the characters move through and about it, as if, by turning around, it too is revealing its inner secrets.

The Browning Version may be better known because of Anthony Asquith's devastating 1951 film starring Michael Redgrave, but the play is if anything even tighter and more intense than the movie. Siân Phillips has done her work for the night and is no doubt enjoying some well-earned rest in her dressing room, but Nathaniel Parker is back again in the central role of Andrew Crocker-Harris, a public school classics teacher on the eve of early retirement. Is he, as the headmaster fondly claims, the "Himmler of the Lower Fifth", or is he a much-loved if curmudgeonly pedagogue? No spoilers here. But once again, this is death by a thousand little cuts, as "Crock"'s world is neatly dissected, crushed and flushed away before his very eyes.

I was so moved during this production that my cheeks were wetter than the glass of Prosecco and elderflower cordial under my seat. The restraint and dignity on display, combined with the heartlessness and cold humour, is an irresistible combination. I left with one of Rattigan's most British lines of all echoing in my head: "It's surprising how cheerful one can be, when one gives up all hope." Chin chin.