Traditionally the theatre has been one of the brightest jewels in Britain’s cultural crown. These days it is noticeably lacklustre. Serious theatre, at least, is a regular disappointment; light West End plays and musicals still give satisfaction to those whose tastes lie that way, but mainstream theatre is often hardly worth the journey or the expensive tickets. For years now, three or four out of every five plays I have seen (excluding Shakespeare productions) have been unimpressive, even poor — particularly among new plays.