Jane Asher, a major character in House, has a three-minute role in Garden

The stages, both in the same building, are separated by three flights of stairs and several corridors.

Characters must maintain the impression they have strolled through a door rather than having run through a maze of corridors.

In Scarborough's Stephen Joseph Theatre, where the plays premi�red, the two stages were much nearer to each other - a mere 35 seconds apart.

'Emergency dog'

Allowances for the time actors need to get between stages are written into the play.

Extra speeches and a device called the "emergency dog" allow whoever is on stage to play for time.

Actress Alexandra Mathie explains: "The dog will bark and one has to respond in character to the dog in some way. So we're discovering our attitudes to dogs as well."

Experiments

This nightmare of synchronisation - the plays must begin and end simultaneously - extends Ayckbourn's experiments with time and space.

In The Norman Conquests, the same events were seen from different perspectives in three plays.

Intimate Exchanges had 16 possible endings and A Small Family Business - recently revived at Chichester - was set on two levels of a house.

The playwright wrote each scene in parallel but says he nearly got mixed up: "The nightmare was ending up with all the actors in one theatre."

Ayckbourn, whose Comic Potential received a nomination for Best New Comedy at this year's Olivier Awards, is best known as a writer of comedies.

But the dramatist finds the suggestion strange: "There's a sort of implication there that if you've written a comedy you haven't written a play - you've written something rather silly."