A curious omission from the Mill at Sonning's programme for its new production of Relatively Speaking is the information - surely not without interest to theatregoers - that Lucy Fleming, one of the four members of its cast, is reviving a role originally created in the West End by her mother, Celia Johnson, writes Chris Gray.

Reviewing Dame Celia's performance at the Duke of York's Theatre in 1967, Irving Wardle of The Times said of her contribution to Alan Ayckbourn's first big hit: "A spectre of baffled gentility with teasingly enigmatic reserves, she gives one of the best comic performances of her career." To the great credit of Ms Fleming, these words are equally appropriate to describe her admirable work at Sonning.

As businessman's wife Sheila archetype of so many bourgeois Ayckbourn heroines she certainly has plenty to be baffled about in the course of this beautifully crafted melange of mistaken identity and multiple misunderstanding.

Who are the young couple so strangely arrived on a Sunday morning in the sunny garden of her luxurious Buckinghamshire home (full marks to designer Katy Tuxford)? Her polite disinclination to ask him direct questions allows Greg (Luke Shaw), who is first on the scene, to persist in the illusion that she is the mother of his girlfriend Ginny (Kate Alderton), while Sheila quickly concludes that he is a business acquaintance of her husband Philip (Francis Matthews).

Confusions multiply with the arrival of Ginny, whom we had briefly met bidding a fraught farewell to Greg earlier in the morning in their scruffy London flat. She told him she was going to her parents for the day. He found their address, as it seemed, and followed in order to ask permission for her hand in marriage. Whoops! The home he was visiting was none other than that of Ginny's sugar daddy lover.

Ayckbourn maintains the level of amusement brilliantly through two acts. Here the cast works so well at the comedy under Alex Scrivenor's direction that at times on Tuesday's opening night there were tears running down my cheeks.

But as I have noted often before, the whole delicate edifice of confusion is seriously in danger of crumbling if you pause to wonder what happens to the characters when they are together offstage.