Thousands of commuters today faced delays after a Tube train struck a bulge in the tunnel wall underneath the Thames.
The Bakerloo line was partly suspended as structural engineers rushed to the scene and there were severe delays across the rest of the line.
The incident sparked a full alert amid fears of a tunnel collapse but London Underground (LU) robustly stressed this would not happen.
The bulge in the wall’s steel plates smashed the train's indicator lights.
The train driver immediately raised the alarm and the line was suspended between Elephant & Castle and Piccadilly Circus.
Structural engineers and emergency services rushed to the scene.
They found a bulge in the wall protruding several inches; it is at a point where four of the huge steel sections of tunnel lining are bolted together.
One theory being investigated by engineers is that a build-up of rainwater - not water from the Thames - following recent storms had raised the water table under London and may have seeped in forcing the plates to bend.
It is understood there has been some recent work on the tunnel walls.
Nigel Holness, LU operations director, stressed: “There is no tunnel collapse in the Bakerloo line, nor is there any flooding or any injuries. It is wrong and irresponsible to suggest otherwise.
“Our engineers and Emergency Response Unit are on site assessing the situation and have advised there is no flooding or risk of flooding or any collapse of the tunnel.
“We are working to resolve the issue and restore Tube services as soon as possible.”
He added: “The problems this morning are not in any way connected with the industrial action taken by some maintenance workers on the Jubilee, Northern and Piccadilly lines, which has had no impact since the strike began.”
It is not yet know if full Bakerloo line services would resume today.
