London Underground has withdrawn several trains from service after they were damaged by incorrectly installed brackets on a tunnel wall.
The brackets, which hold pipes in place, scraped along the side of the trains, damaging the outer skin and breaking windows in some carriages.
There were no reports of injuries after the trains struck the brackets between Farringdon and Barbican stations.
LU said three trains had been withdrawn from service, after "unsecured" brackets caused minor damage.
Bobby Law, the RMT London organisers, said the oversized brackets had been installed by subcontractors.
"This is another example of the dangers in PPP with the complex web of subcontractors," he said.
The Tube's safety system was not coping, and the RMT wanted an inquiry into the working of the PPP system, said Mr Law.
The Hammersmith and City, Metropolitan, and Circle lines were suspended for an hour yesterday after the trains were damaged about 8am.
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