Workers digging up the streets are risking electrocution because power distribution companies do not know the exact location of their underground cables, according to Britain's safety regulator.
The Health and Safety Executive (HSE) has written to the energy regulator, Ofgem, urging it to act quickly to tighten lax regulations.
These mean the electricity companies do not need to keep data on all their power cables, many of which run below pavements and roads.
HSE figures show that since records began nine years ago, six fatal accidents have occurred as a result of the poor record-keeping. A spokesman admitted that the real figure could be much higher. Almost 250 non-fatal but serious incidents were recorded in that time, he said.
The HSE began reviewing regulations covering the laying of power cables in 2003 but shelved the investigation late last year because it did not have the resources to complete the work.
The powers of the executive, which is responsible for regulating the workplace, have been restricted by industrial action. Many safety inspectors at the HSE are refusing to work overtime in protest at low pay.
Ofgem is now consulting on the first major review into the way electricity grid companies operate.
In a letter to the regulator last month, an HSE adviser said that the situation was becoming more pressing as the number of power cable operators proliferate. "Electric cables are often discovered during excavation and construction activities. These are sometimes no longer in use but still energised, making any cable strike a potentially serious hazard. More extensive records would ... ensure that persons not in their employment are not exposed to risks to their health and safety," the letter said.
Ofgem will publish the results of its review next month. A spokesman said mapping power cables was primarily a safety issue and therefore fell under the remit of the HSE. He declined to comment on the contents of next month's review.