Hour-long delays for commuters yesterday may have been caused by a burnt cable feeding a signal control box, South West Trains (SWT) has said.

A final verdict on what caused damage to signals in the Wimbledon and Earlsfield area has yet to be reached, the operator said.

But bosses apologised for the rush-hour delays, the latest in suburban London's ongoing saga of railway failures.

Customer service director Arthur Pretorius said in a statement: "I am very sorry for the serious disruption that many of you will have faced whilst travelling on our services on Wednesday morning.

"At about 4.30am we had reports of a problem at a signal control cabinet located between Earlsfield and Wimbledon.

"All signalling and safety equipment in the area was affected and we were unable to run trains.

"The reason for this damage is still being established however initial investigations suggest that it was caused by a burnt cable feeding the signal control cabinet.

"The incident meant that many trains were unable to leave train depots to start their journey on time, and those that had already left the depot were unable to continue their journey.

"Engineers found and rectified the problem at 6.30am and our team worked extensively to ensure that as many of our services as possible could run throughout the morning, and that we were able to have our normal service operating ready for the evening peak."

Delays affected commuters on all routes in and out of London Waterloo.