A defect on Tube trains on the Piccadilly Line is threatening safety on London Underground just days after Saturday's crash, BBC London has learnt.

There have been three incidents since November where trains have had to be taken out of service after carriages filled with smoke.

The problem is believed to be caused by axle bearings wearing out prematurely. On at least three occasions the axles have seized up.

This comes as London Underground (LU) continues its investigation into why a Central Line train jumped the tracks and hit a wall at Chancery Lane station at the weekend.

Obviously they have known about this situation for a long, long time and we would have hoped that they would have put in measures some time ago Bobby Law, RMT

BBC London's Transport Correspondent, Andrew Winstanley, said the latest problem appears to be just on the Piccadilly Line.

He said: "The axles of the trains are overheating because bearings have failed, so effectively the axles can't turn around properly and they overheat.

"That causes all sorts of problems with burning rubber under the train filling the carriages with smoke.

"Clearly the RMT union see this as a serious safety problem."

'Facing disaster'

He added that the problem "could ultimately derail a train".

The worst incident was last November at Kings Cross, where two Tube drivers were taken to hospital after inhaling smoke.

Bobby Law, from the Rail Maritime and Transport union (RMT), said: "We could be facing a disaster now not just on the Central line but also on the Piccadilly Line.

"Obviously they have known about this situation for a long, long time and we would have hoped that they would have put in measures some time ago."

London Underground told BBC London they are managing the problem.