London commuters were left stranded by the power cut

Radio 4's Today programme said August's power cut was caused by poor maintenance of the supply network by National Grid Transco.

A senior executive at the company has denied the accusations saying its report into the event had been thorough and open.

But an engineer, who did not want to be named, told the programme there were insufficient staff to carry out maintenance work.

The investigation pointed to a long term oil leak at a sub-station being the cause of the blackouts.

It is not poor maintenance Nick Winsor, National Grid Transco

Commuters faced chaos in London on 28 August when the Tube system was brought to a virtual standstill by the loss of power.

Around 600,000 homes and businesses were also plunged into darkness.

The report by Transco said the cause had been the incorrect installation of a one amp relay instead of a five amp relay.

Nick Winsor, director of transmission for National Grid Transco said: "We did know that there was an oil leak, it had been registered, and the leak had been topped up.

Checks backlog

"This had only been reported a matter of a few weeks before. It is not poor maintenance.

"That equipment is there for a purpose and particularly in summer it is there to control the voltage and we can't just take equipment like this off the system immediately."

Mr Winsor also answered accusations about a backlog of statutory checks on the network.

He said: "These particular inspections are at a frequency which is determined by us consulting with an independent engineer and, in centralising all of the paper based records on to a new electronic database we have found an issue here, which is a small backlog which we will have fixed by Christmas."