'Power safety margin is razor-thin'

Serious and deep-rooted faults in Britain's power supply have been exposed by London's blackout.

Leading government adviser Professor Ian Fells, who first highlighted his concerns after the New York blackout, said: "We are operating with a vastly underfunded system running on razorthin safety margins."

It is still unclear what caused the blackout. It is believed transformers failed on the 275,000 volt power lines used to bring electricity from power stations around the UK to the edge of London.

This caused power to a circuit serving Wimbledon, Hurst and New Cross to fail. Further problems occurred due to the time it took to bring this circuit back online.

A spokesman for National Grid Transco (NGT) said: "It's rather like having to re-boot your computer. It's making sure the systems are working properly before we put the big bulk supplies back on to the system."

Operated by NGT, the high power lines that are believed to have failed form the backbone of the grid that feeds power to the whole of the UK.

These high voltage lines feed into a second, lower voltage grid operated by EDF Energy, which is responsible for taking power to homes and businesses around London and the South-East.

London Underground, however, has its own deal to receive power directly from the national grid. Until last October it operated its own power station in Lots Road, Battersea. This closed following a £108 million government-backed private finance deal.

EDF Energy confirmed its system had not caused the failure, and had operated correctly throughout the blackout. A spokesman said: "We are waiting for an explanation from National Grid Transco ourselves."

NGT refused to speculate on the exact cause of the blackout, claiming it would need to complete a thorough investigation.

Power experts believe the failure of the high power supply lines revealed a glitch in the computer software that operates the power grid.

Professor Fells said: "It appears a software glitch in the the computers that run the grid failed, causing the loss.

"Originally it seems the problem was a transformer failure, but that's pretty common and should not have caused this amount of trouble. It was really a mini New York, with a small fault cascading into a larger one. I think we were actually quite lucky - this could potentially have wiped out power all around the UK.

"So many of our power stations have been mothballed for financial reasons that we are operating right on the edge of safety margin. Twenty years ago, we kept reserves of up to 28per cent. Now they are into single figures."

Electrical engineering expert Dr Tim Green, from Imperial College, said: "Events like these are normally caused by a mismatch in supply and demand, if you don't have enough supply it can cause a dramatic collapse."

Four years before Lots Road was sold, a 30-year contract for providing the Tube's power had been given to Seeboard Powerlink (SPL), requiring it to "manage, maintain, develop and finance" the system. SPL, made up of electricity company Seeboard, construction giant Balfour Beatty and technology company ABB, provided finances to upgrade the technology to allow the Tube to take power directly from the National Grid.

But in the event of a failure, a smaller power station at Greenwich - equipped with "quick start" gas turbines - was to be used for emergency power. SPL also installed battery lighting at all stations for use in an emergency. During the first five years of the contract, SPL was required to install equipment to provide emergency supplies to the railway "in the event of a major power failure".