London's mayor, Ken Livingstone, has warned that he will veto plans for Britain's first £1bn private finance initiative hospital unless its design is "substantially improved".

Under a PFI project St Bartholemew's and Royal London NHS trust have submitted plans to Tower Hamlets council to rebuild the Royal London hospital in east London as coloured glass blocks of up to 18 storeys high.

The mayor can reject major building projects of this scale, even if they have been approved by a local council.

Last night Mr Livingstone's office wrote to Tower Hamlets to warn that if it approved the building in its current form he would overrule that decision.

Mr Livingstone said: "Plans for a new Royal London hospital are a unique opportunity to transform healthcare facilities for east London. The design of the new buildings must be substantially improved to give east London the hospital it deserves.

He added: "This hospital will dominate the local area and affect the lives of east Londoners well into the next century. They have every right to expect that their new hospital meets the highest possible standards. But the current proposals fall short."

Mr Livingstone's threat comes after the government's architecture watchdog, the Commission for Architecture and the Built Environment, delivered a scathing attack of the design of the building.

On Tuesday, it said the building could recreate the kind of public building mistakes made in the 1960s.

Like Cabe, Mr Livingstone is concerned about the complex layout of the design. He pointed out that patients and other visitors would find it confusing and alienating.

He went further by adding layout could even encourage antisocial behaviour.

The mayor is urging the trust and its PFI consortium Skanska Innisfree to have immediate discussions with his officials and Tower Hamlets council to come up with improvements.

On Tuesday, the trust and Skanska Innisfree rejected Cabe's criticism of the scheme. Barts and the London NHS trust's chief executive, Paul White, said it would deliver "first class 21st century facilities".