CONCERNS have been raised about an electricity firm's plans to dig 50 metre deep holes in green spaces including a nature reserve.

The National Grid wants to carry out works on Walthamstow and Leyton Marshes as part of a seven-year project to install new power cables deep underground.

It plans to drill a tunnel all the way from a substation near the Hackney side of Lea Bridge Road to the marshes before curving north west through Stamford Hill and Finsbury Park, but the firm said it needs to investigate the earth first.

The company says it will dig a series of boreholes, which will be 50m deep and 30cm wide, along the route.

The areas affected will be fenced off while work is carried out and the holes will be covered when completed. However staff will return to them “occasionally” to check on them in future.

The National Grid says works in Waltham Forest will take around 26 days to complete, but has not provided details of the exact locations or when the digging will take place.

It is also unclear how many holes it plans to dig.

Environmentalists have expressed concern about the impact of the works and say it is another example of further meddling with north east London's wild green spaces.

It comes after complaints about a temporary sports hall built on Leyton Marsh during the Olympics, where the land is yet to be returned to its original condition as promised by Games bosses.

Caroline Day, of the Save Leyton Marsh campaign, said: “Our concerns are not just about what the National Grid wants to do, it's more that previously undisturbed green spaces are becoming increasingly interfered with.

“There's an attitude now that these agencies can dig up land and then just put a bit of turf on the top afterwards and expect everything to return to normal.

“But if a wild habitat is disturbed then some species will often never return, which is particularly bad when they are rare.”

Campaigners are also concerned by the National Grid statement's that the underground tunnels “will significantly reduce disruption to the local area as we are able to lay the cables and carry out maintenance work without digging up the road network.”

Ms Day said: “If their main motivation is not to disturb the road network then that is a genuine concern, it says a lot about their priorities. And it raises questions about if they will dig up the marshes again in future”.

The National Grid says the new cabling is necessary for it to keep up with rising demand for electricity in London.

A spokesman said: "On a complex engineering project such as this, it is vital that we have a detailed understanding of the ground conditions we will be tunnelling through.

"Therefore a series of boreholes have been dug along the tunnel route to ensure we have accurate and reliable ground condition information.

"Our borehole investigations at the Leyton and Walthamstow Marshes are part of this work and will take approximately 26 days to complete."

He added: "National Grid is committed to treading carefully wherever we carry out our work.

"We always endeavour to deliver our vital work as sensitively as possible and are always mindful of the natural environment."