The pylons from the new plant next to Sellafield will be visible from the Lakeland fells

Campaigners have condemned a decision to build power lines on pylons up to 50m (164ft) high through the Lake District national park.

National Grid announced its plans to route its electricity transmission lines from a new nuclear power station partly within the national park.

The Friends of the Lake District said the cables should have been directed offshore.

National Grid looked at various options for the route of the new lines, including under the Irish Sea, but dismissed this as too risky. It decided to take a line north along the Cumbrian coast before heading inland near Maryport to a substation near Carlisle.

But it is the southern arm of the route which caused concern for the Friends. It will enter the national park near Ravenglass then head towards Broughton in Furness before going under Morecambe Bay to a new substation near Heysham.

The conservation charity said the new pylons could cause major damage to the Lake District’s landscape. The proposals are for overhead high-voltage lines for 20km (12½ miles) within the national park and a further 24km (15 miles) alongside its boundary.

Kate Willshaw, policy officer at Friends of the Lake District said: “We are obviously deeply disappointed by the choice of Onshore South with Tunnel over the offshore route, especially as the majority of the 1,200 consultation responses received supported the offshore option.

“National Grid’s own environmental study supported taking the cables offshore to avoid the Lake District as their chosen route runs through or close to the national park for 27 miles.

“It is vital that National Grid engage with local communities and the many organisations that live, work and care for these great landscapes to discuss how to mitigate the damage their proposals could cause.

“We know our 10,000 members and supporters feel very strongly about a new pylon line damaging the national park. National Grid’s own consultation demonstrated the strength of public opinion; the majority of the 1,200 respondents wanted to see the route go offshore and avoid these sensitive landscapes altogether.”

National Grid said work will now start on determining the exact route within the chose corridor and some existing power lines will be taken down and replaced with higher capacity ones to serve the new nuclear power station at Moorside near the existing Sellafield facility.

It said the company chose the corridor after five years of discussions with national and regional bodies and thousands of conversations with people during a consultation exercise last autumn.

Project manager Robert Powell said: “We had thousands of conversations with people during autumn of last year and some key themes have emerged.

“People understand how important it is for us to connect new sources of generation into the grid and the task we face in doing this in a region with some of the most spectacular landscapes in the country.

“Many people think that following the path of existing power lines and taking these down to replace them with our own equipment is a good idea. There is support for our plan to cross under Morecambe Bay and this would avoid building a connection through the South Lakes.

“There are also a lot of people who would like us to put cables out of sight on the sea bed between Moorside and the Lancashire coast. We explained at the start of consultation that this wasn’t our preferred option. We’re not taking this forward for several reasons.

“NuGen, the company which is building Moorside, prefers the route we have chosen. They share our concern that offshore high voltage direct current cables have never been used to connect a nuclear power station. Using this untried technology could introduce risks for the Moorside project.

“The sea bed in this area is already congested with cables, gas pipes and wind turbines. There are thousands of rounds of unexploded ordnance out at sea from the Ministry of Defence’s Eskmeals firing range. Also, if an offshore cable develops a fault, it can take up to six months to repair.”

National Grid said it is now starting to talk to landowners and communities along the corridor it has selected about the technologies it can use to build the connection and possible locations for the equipment. Several areas were identified during the consultation as requiring further close study including the Duddon Estuary and near to Whitehaven.

Mr Powell said: “The conversations we are continuing to have with people remain very important as we start to pinpoint the exact route that the connection will take.

“We’re starting discussions with landowners that will help us put a line within the corridor to show exactly where the new connection could run. We will be holding a series of community events in the autumn to share a draft version of this line along the corridor so people can give us any information that could influence the design of the route.

“This will allow us to refine the alignment further before we start more formal consultations next year.”

The company aims to submit an application for consent to build the new connection to the Planning Inspectorate in 2017. A decision will then be made by the Secretary of State for the Department of Energy and Climate Change.

If consent is granted, construction work is expected to start in 2019. National Grid said it is required to provide NuGen with the first phase of the connection into its transmission network by 2024.