A triple explosion in underground cables outside Sutton train station this morning caused the powercut that sparked major disruption in the town centre.

Quadrant House office block, the council offices, Morrisons supermarket, and Sutton train station all suffered blackouts after the three small blasts in the power cable.

The pavement ruptured in front of commuters from the force of the blasts. Witnesses described hearing three bangs at about 9.10am.

Although the station remained open, but without announcement screens, a cordon was put around the area of impact as engineers explored the cause of the blasts.

A crack by the lifts on the platform directly below the rupture was also thought to have been caused by the blasts.

An engineer from UK Power Networks, Mike Mcloughlin, said: "We have a 11000 volt HV cable which has exploded under the ground. It could have happened for many reasons, for example it could be an old cable, we just don't know yet."

A spokesperson for Southern Trains, which operates the station, said: "It is an issue with the local power supply, an electricity cable popped outside the station. We hope it is resolved as soon as possible."

Thousands around the borough were affected, including businesses on the high street. UK Power Networks said in total 435 of its “customers” lost power.

Morrisons was plunged into darkness and had to turn away customers between 9am and when the power eventually returned just over an hour later. A member of staff who did not want to be named said he feared the store would lose hundreds of thousands of pounds of stock as the fridges and freezers were out of action, but power returned at about 10.30am.

Fire fighters briefly attended the scene.

A spokesman for UK Power Networks said: "At 9.12am today (April 25), 435 customers in The Quadrant area of Sutton experienced an interruption to their power supplies because of a fault on the high-voltage underground electricity distribution network.

“We appreciate how difficult it can be to lose power and would like to apologise for the inconvenience caused by this incident."

A spokesman for the engineering company said that all electricity was restored by 11.20am.