The pipework gracing the outside of the distinctive Lloyd's insurance building in the City of London is rusting away just nine years after it was completed.
Emergency inspection is now under way. Managers of the building -dubbed the "espresso machine" because of its appearance - have instructed solicitors and may begin legal action against the designers or contractors to recoup the cost of remedial work.
But yesterday the architects, the Richard Rogers Partnership, denied liability and said they would vigorously defend any legal action.
The consulting engineers, Ove Arup and Partners, who designed the technical specifications for the pipework, merely said they were aware of the problem.
Severe corrosion was discovered in the hot water pipes which power the central heating system of the 12-storey building some time ago and work to replace those affected pipes has been going on for about a month.
The hot water pipes seem to be worst affected because of the temperature differential, though Lloyd's management has also begun inspections of the cold water and air-conditioning ducts to establish if they, too, need repairs.
The crisis over the landmark of modern British architecture follows controversy over massive losses for investors in the insurance market.
A spokesman for Lloyd's said the problem was discovered during routine inspection and rust was found on the external service pipes.
Nick Phillips, Lloyd's general manager, yesterday declined to disclose the likely cost, except to say that like, everything in the City, it would be expensive.
However, he said he believed that he would recover all the costs of the repairs to the pounds 187m, award-winning building once it had been determined who was responsible.
Mr Phillips said that the City solicitors, Herbert Smith, had been instructed but no writs had yet been issued. He hoped that ultimately the company or companies responsible would "hold up their hand".
Michael Davis, a specialist construction lawyer, said writs were likely to be issued by the end of the year and the damages claimed would be "substantial".
He added: "We will be carrying out a full review of all the parties who were involved in the 1986 building to see who could be remotely connected with this failure.
"Lloyd's intention is that proceedings will be commenced and I would think that these proceedings are likely to be commenced before the end of the year."
The contractor, Ove Arup, said it could not comment on the claims until the inspection was complete.
Helen Murphy, of Ove Arup, said the company was aware of the repairs and investigations, but regretted that Lloyd's had adopted an "adversarial approach" to the difficulties.
Martin White, company secretary to the Richard Rogers Partnership, said he was aware that Lloyd's had discovered a problem with the pipework.
But he added: "Investigations are taking place to ascertain the cause of the problem. Richard Rogers Partnership do not believe that the problem is a design problem. If proceedings are started they will be strongly defended."