The gas pipe was fractured on Monday afternoon

The organisation has called for a government inquiry into a major leak in County Durham on Monday, after which about 2,500 homes remain without gas.

A pipe was ruptured near Spennymoor during work to modernise the network.

Northern Gas Networks and industry watchdog Ofgem both dismissed the GMB's comments, saying there was no evidence safety levels were anything but high.

Engineers were working to replace old, cast-iron gas pipes with modern, plastic ones at Middlestone Moor when the leak occurred.

There is no evidence of a deterioration of reliability in the gas network Mark Wiltsher, Ofgem

An investigation into the cause of the incident, which at its peak left 10,000 people without gas, has been launched.

GMB spokeswoman Joan Anderson said: "The current system of regulation is failing consumers and endangering lives.

"We consider that the growing use of sub-contractors and the fragmented way the distribution network is being managed is undermining public safety and the security of gas supplies."

The leak has been repaired, but residents now face a long wait as engineers must visit each property to carry out safety checks.

Northern Gas Networks spokesman John O'Grady said: "Safety management in the gas distribution network is the responsibility of the Health and Safety Executive.

"Contractors have been used in the industry for generations, working alongside other dedicated engineers. We have full confidence in all our contractors."

'Replacement project'

About 60% of affected properties should be reconnected by Thursday night, according to the company.

In the meantime, Wear Valley District Council has taken emergency measures to ensure vulnerable areas such as care homes have adequate heating and cooking facilities.

Ofgem spokesman Mark Wiltsher said: "There is no evidence of a deterioration of reliability in the gas network. In fact, the evidence points to the reverse.

"At the moment there is a replacement project under way to replace cast iron pipes which should make the network even more reliable."

Ofgem were unable to comment on the Middlestone Moor incident while an investigation was ongoing, he added.