John Mortimer, frail and virtually wheelchair-bound as he nears his 85th birthday, presents such a genial face to the world, both as man and writer, that it would be dangerously easy to regard this Legal Fictions bill of two short plays, The Dock Brief (1957) and Edwin (1982), as some sort of last hurrah for conventional West End standards.

It’s true that neither piece, in which Edward Fox plays first a failed barrister and then a retired High Court judge, comes at you with the buttonholing intensity of Sarah Kane or Mark Ravenhill. But in their own way, they stand for decency, fair play and a largeness of spirit that characterise their author in his lifelong defence of free speech.

Designer Mark Bailey provides Christopher Morahan’s elegant production with a theatricality essential to plays which started out as radio drama; in the first, the fidgety little wife murderer and birdseed shop owner, Fowle (Nicholas Woodeson), receives his allotted barrister, Morgenhall (Fox), in a vaulted cell of white tiles and high windows that allows the couple to invent their own mock rehearsal; in the second, Sir Fennimore Truscott (Fox) ponders on his neighbour Tom Marjorybanks’ (Woodeson) affection for his wife Margaret (Polly Adams) on the lawn of a handsome house and conservatory in the shade of an old mulberry tree.

Fowle killed his wife because her jollity drove him bananas and she spurned the opportunity of running off with the lodger. Truscott’s opening line in Edwin – “I put it to you, Marjorybanks, you rogered my wife” – sets out a scenario of adulterous possibilities and paternal identity questions on the very day that his son Edwin – a long absent, high-flying manager in Global Computers – is coming to lunch (we never meet him).

Fox plays Morgenhall as a tragic eccentric who failed in love just as he fails in his first-ever “dock brief” after waiting years to be summoned. His Truscott, dapper and spry in a brown trilby and cardigan, is a social relic with an unshakeable belief in his own place in the world. Watching Fox is like watching an alien comedian of the old school, AE Matthews, perhaps, or Alistair Sim. His vowels are strangulated almost to the point of incomprehension, his jaw clamped rigid like a man whose dentist has left a full set of implements in situ, his gestures despatched with airy ambiguity.

This cranky carapace flatters to deceive, however, for Fox is a master of timing and an actor of sudden, touching sensitivity. The earthbound, highly effective performances of Woodeson and Adams are satellites to his potty planet of otherworldliness from which he radiates a charm as weird as it is strangely moving. You may never see this type of acting again.

- Michael Coveney