Theatres contribute about �1.5bn to London's economy every year.

The area's 40 venues were all built before 1937 and many are in "desperate need" of repair works.

The investigation concluded that there was no single solution to tackling the long-term under-investment.

But it warned that the diversion of lottery money to the 2012 Olympics would add pressure to funding bodies.

The assembly's Economic Development, Culture, Sport and Tourism Committee suggested ideas such as a ticket levy, corporate sponsorship, fundraising campaigns and debentures.

There does need to be a willingness among theatre owners to take a more creative approach and look at options that they may not previously have considered Bob Blackman, report author

While some like the Gielgud have benefited from private investment, others, including playhouses such as the Garrick, have a lack of toilet facilities, bad seating and poor sightlines, as well as structural and aesthetic works, the report said.

Bob Blackman, who led the investigation, said: "The issue of securing funding for improvements to West End Theatres has reached an impasse and for most theatre owners the last five years of debate have thrown up no answers.

"This report offers a range of viable options. But there does need to be a willingness among theatre owners to take a more creative approach and look at options - or a combination of options - that they may not previously have considered," he added.

Theatre audience numbers are now at record levels and contribute about �1.5bn to London's economy every year.