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A £1m robot will today complete work repairing gas mains in London without having to dig a single hole in the street in a UK first that it is claimed will save thousands of hours of disruption to motorists.

Scotia Gas Networks, which operates as Southern Gas Networks, completed the upgrade of a half-mile stretch of road outside Woolwich barracks, south London, in 20 days compared to the three-months it would have taken using the old technique of digging trenches in the road and carrying out the repairs by hand.

Invented in the US, the CISBOT - cast-iron joint-sealing robot - is launched underground from a “keyhole” at the roadside with no interruption to gas supplies.

It is directed from a nearby cabin by handlers using Underground cameras and lasers to pinpoint leaks.

With a reach of 300 metres, the robot travels inside the pipe and injects a long-lasting sealant into the 91 decaying joints of the 100-year old pipes in a job requiring just four workers.

Without the “keyhole” technique, around 30 holes would have been dug along the route which weaken the road structure and can cause potholes.

Robot repairs have been used for the streets of New York and Boston since 2010, but Woolwich is the UK pilot. CISBOT will shortly go underground in Highgate, north London in a gas mains repair job for National Grid.

Robotic working under the capital’s streets comes after the mayor last year introduced a lane rental scheme which can charge utility companies thousands of pounds a day for digging up key routes. Last week Thames Water was fined nearly £14,000 for causing unnecessary disruption during roadworks.

CISBOT was brought to the UK with an innovation grant from industry regulator Ofgem and it will be shared with other utility firms.

But its owners ULC Robotics say it is uniquely suited to working in gas mains and caution that there are significant obstacles to working on other underground utilities such as water, electricity and telecommunications.

Sam Wilson, Scotia Gas Networks project manager for the Woolwich pilot, said: “By working with the robot, we can drastically reduce disruption to motorists and businesses. The local shopkeepers didn’t even know we were here. It saves money for the company, avoiding mains replacement because the maintenance work has increased the pipe’s lifespan by 50 years.”

Isabel Dedring, deputy mayor for transport, said: “We’re delighted to see major utility companies such as SGN responding to our lane rental scheme and using new technology to help reduce the disruption caused by roadworks. Charging the utilities for using our busiest roads has been a key factor in helping them to choose more innovative, less disruptive techniques - some of which have never been used in the UK before. Measures like this could save Londoners thousands of hours of disruption each year if rolled out across the capital and we’ll be pressing more companies to adopt them as a matter of course.”

SGN Network Director Paul Denniff said: “We feel that the project demonstrates our commitment to embrace the principles laid down by our regulator Ofgem to work in the most efficient way. We really want to transform the way we work in the street – we want to develop innovative solutions to repairing pipes which are causing us issues, rather than digging lots of holes in the ground.”