LONDON (AP) — This is not a metaphor: Britain's Parliament is a mess.

The 19th-century building is crumbling, leaky, infested with vermin and riddled with asbestos. Fixing it will take years and cost billions, but experts say the alternative could be catastrophic.

After years of dithering, lawmakers are set to vote Wednesday on what to do, and there's a good chance they will opt for more delay.

Experts have issued increasingly urgent warnings about the state of the neo-Gothic Parliament building, one of London's most famous landmarks and a UNESCO World Heritage Site. Reports have sounded alarm bells about leaky roofs, temperamental steam heating, antiquated plumbing, crumbling stonework and ventilation shafts clogged with old pipes, wires and asbestos.

A 2016 report commissioned by parliamentary authorities said the building is at risk of a flood or fire that could leave it uninhabitable. It advised members of the House of Commons and House of Lords to move out for six years for renovations, estimated to cost about 3.5 billion pounds ($5 billion).

Caroline Shenton, former director of the parliamentary archives and author of "The Day Parliament Burned Down," said that without major repair work, Britain could lose "the most iconic, famous building in the country."

"It could just simply be a utilities failure that brings the whole thing to a halt — the electricity goes, the water stops working, the loos stop flushing," she said. "But something more catastrophic could happen."

David Leakey, who retired last year as Parliament's head of security, has said that without major work Parliament could be "another Grenfell Tower" — the London high-rise that burned down last year, killing 70 people.

Despite the warnings, lawmakers have put off making a decision. Some worry the public will resent the expense. Traditionalists are reluctant to leave the historic Commons and Lords chambers, the subsidized bars and restaurants and the riverside terrace with its magnificent view across the Thames.

Some modernizers think a permanent move to a new building — perhaps even one outside London — would make politicians less out of touch with the people they serve.

Lawmakers will vote on several options, from agreeing to move out by the mid-2020s to deferring a decision for several more years.

The seat of Britain's government has stood on the same riverside site for centuries. The oldest surviving part of the complex, Westminster Hall, is 900 years old. But the current building, designed by architect Charles Barry, was built after fire destroyed its predecessor in 1834.

Shenton said authorities had debated what to do about their aging building for years before the 1834 blaze. She hopes today's politicians learn from their predecessors' indecision.

"Nobody could make a decision," she said. "In the end, the decision was made for them."