A levy on West End theatre tickets may be needed to save some of London's historic buildings.

The move would mean even higher prices to preserve Theatreland's heritage and make venues comfortable for 21st century visitors.

The admission was made by Nica Burns, the co-owner of five theatres and producer of shows such as the Christian Slater hit Swimming With Sharks.

In response to early findings from a London Assembly inquiry, she said serious measures were needed to secure the future of the capital's important venues.

The London Assembly is investigating what can be done to save theatres - most built in the Victorian and Edwardian eras.

A report by the Theatres Trust four years ago said they were in desperate need of an estimated £250 million modernisation. Early leaks from the new inquiry yesterday suggested that a surcharge on ticket prices may be the answer.

Bob Blackman, who is heading the investigation, told The Observer: "There is definitely potential for a ticket levy to be introduced because there has clearly been under-investment for many years."

Producers who hire venues take the box office receipts - not the theatre-owners - so a surcharge would have to be transparently separate. But Ms Burns said the bottom line was improvements were required.

Yet while impresario Sir Cameron Mackintosh had invested millions of his own money in improvements, Ms Burns said the economics of theatre made that impossible for most owners and producers. The four major playhouses in Shaftesbury Avenue, for example, are said to have taken only £30 million between them since the Second World War.

"If I had the money to do it [make improvements] I would, but I don't. But it's a problem that needs to be solved so we have to look at the different ways," she said. "The West End is vital to London so I would love to hear what ideas people have."

Moira Samuel, chief executive of the campaigning Theatres Trust, said there had been patchy investment in the West End so far.

The commercial sector has been "ready to play its part" but what was needed was public money to support the economic significance of theatre to culture, heritage and tourism. The London Assembly launched its investigation to identify practical solutions for the modernisation of West End theatres in September.

It is due to report early next year.