THERE'S every reason to believe — if we turn a blind eye to Mr and Mrs Trump’s rather depressing union — that a significant difference in age between two people is no particular hindrance to an enduring and happy relationship.

It’s the thesis of Martin Sherman’s play, directed by Sean Mathias, about the tribulations of intergenerational love. In it Rufus (Ben Allen), a twenty-something young professional struggling with bipolar disorder, pleads with Beau (Jonathan Hyde), a sixty-something pianist from the Deep South in the US, not to forget about him after the hasty tryst they arranged online.

Indeed, he’d like them to spend more time together and perhaps even embark upon a relationship. But Beau has his doubts: “You wanted a daddy,” he protests to Rufus, “but soon you’ll have a grandaddy.”

How does he know that Rufus — in spite of his assertions to the contrary — won’t promptly fall for someone his own age? But Rufus is persistent, and soon moves in.

Years pass and, in spite of Beau’s reservations, a happy relationship blossoms, though one punctuated with the lows of Rufus’s condition and the pathos revealed in Beau’s soliloquies, where he remembers his formative years as a gay man.

He tells of the evening he lost a partner in the UpStairs Lounge gay bar in New Orleans that was torched one busy night — this actually happened and was met with apathy by the local authorities.

And he tells us too about New York when the Aids crisis raged, leading to the death of another loved one. The question is, of course, will he now lose a third?

It’s no spoiler to reveal that his fears come true, with Rufus one day announcing that he has met another, younger, man — a plot development that drew an audible sigh from Sir Ian McKellen, sitting next to me.

But when whippersnapper Harry (Harry Lawtey) arrives on the scene, events don’t prove to be quite as traumatic for Beau as you might think.

As he witnesses the pair enjoy the “privileges”of marriage and children denied to gay men of his generation, Beau discovers a role for himself in the lives of others that doesn’t hinge on his existence as a sexual being.

And that, in Gandalf’s immortal words, “is an encouraging thought.”

Runs until March 16, box office: parktheatre.co.uk.