Thousands of commuters and Olympic spectators were hit this morning when the Central Line was put out of action across east London during the whole of rush hour.
Services were suspended for three hours between Liverpool Street and Woodford, leaving passengers stranded at Bethnal Green and Stratford.
A driver reported smelling smoke on a train as it pulled into Leyton, one stop north of Stratford.
Meanwhile, the RMT transport union called for an immediate investigation into "the real impact of cuts to fleet maintenance schedules" following the incident.
The union said it was emerging that the likely cause of today's problem was defective brakes seizing up.