A long awaited report published by an organisation associated with National Grid says pylons are cheaper than burying power cables.

But campaigners have taken heart as it is not as expensive as the power giant had originally claimed and they have already found evidence in favour of their arguments.

The firm wants to build new pylons across the Cheddar Valley to carry electricity from the planned nuclear power station at Hinkley Point to Avonmouth.

National Grid said they welcomed the publication of the independent study on transmission costs prepared by Parsons Brinckerhoff and endorsed by the Institution of Engineering and Technology (IET), saying it “will be a valuable contribution to the public debate” and is “broadly in line with the costs that National Grid has been quoting”.

The report runs to hundreds of pages but finds that the pylons cost between £2.2 million and £4.2 million per kilometre while putting the cables underground is between £10.2 million and £24.1 million. Digging a tunnel, they say, would run to anything between £12.9 million per kilometre and £23.9 million.

The report goes into exhaustive detail on all aspects of the practicalities and cost implications with definitions of how they arrived at the figures. The authors emphasise cost ratios are volatile.

Previously campaigners from Mark to Sandford have estimated the costs as amounting to around £1 extra per household bill to bury the cables.

The figures were immediately dismissed by campaigners as being exaggerated. No Moor Pylons’ chairman Paul Hipwell said: “The report makes clear there is no one answer – undergrounding is just as possible as pylons – it all depends on the local situation.

“The report shows that the cost of undergrounding is substantially less than what National Grid has been saying. The report also says the cost of undergrounding technology especially Gas Insulated Lines (GIL) is reducing and will continue to reduce.

“We want National Grid to halt their current plans. Stop and reconsider what is the best solution for Somerset.”

Mark resident and anti-pylon campaigner Maggie Gregory said: “All along we have been saying that the cost of undergrounding is less than what National Grid have been saying.

“National Grid is out of date, this report says that the cost of undergrounding is lower than they’ve been saying and that the GIL technology is a viable alternative.”

Weston MP John Penrose, whose constituency villages lie near the path of the power corridor to Avonmouth, said: “This is a heavyweight independent report which makes clear that cost isn’t the only factor in choosing the technology, and that underground cables are the next cheapest option after pylons.

“Given that the Mendip Hills are an Area of Outstanding Natural Beauty (AONB) which we have to preserve for future generations, I think this strengthens the case for underground transmission. After all, if the AONB isn’t worth preserving, where is?“

Wells MP Tessa Munt said: “The report runs to more than 300 pages so I will need more time to brief myself thoroughly.

“We, the anti-pylon campaigners and I, always suspected that it wouldn’t be 17 to 20 times more expensive to put cables underground, as National Grid asserted originally. This report confirms exactly that – it is only five to six times more expensive to bury the cables.

“I particularly welcome the report’s first main finding, which states ‘No one technology can cover, or is appropriate in, every circumstance, and thus financial cost cannot be used as the only factor in the choice of one technology over another in a given application.’”