Richard Pulford, chief executive of the Society of London Theatre - which represents producers, theatre owners and managers - said: "People's expectations have gone up quite sharply in recent years.
"Clearly there are some problems and we are working to solve them. We have to solve them. We are, however, encouraged that people still view their visit to the West End as good value for money.
"Their opinions on individual performances will obviously vary... but their opinion on value for money is the bottom line. If that declined, we would see it as an imminent warning.
"We are increasing the number of offers available to young people and hope they can be tempted back in larger numbers."