The driver's union Aslef said it was "sympathetic" over the problems being faced by London Midland.

BBC: Arrivals board

Train drivers union Aslef, however, said it was impossible to rule out further shortages in future.

BBC: London Midland rail operator 'let passengers down'

Mick Rix, general secretary of Aslef, said he welcomed the intervention of the mayor.

BBC: Tube strikes called off