Campaigners fighting plans to erect a new 400,000-volt power line across the North Somerset countryside are calling on National Grid to go back to the drawing board.

The calls have been made after an independent report revealed the cost of undergrounding cables is not as expensive as the energy giant first estimated.

The report, commissioned by the Infrastructure Planning Committee (IPC), looked at the costs of various options for installing the new power line from Avonmouth to Hinkley Point

It analyses the whole life costs of installing and maintaining new high voltage transmission circuits under the ground, under the sea and over ground.

National Grid says the line – a large section of which will cross the North Somerset countryside – is needed to bring electricity onto its transmission network as part of the Hinkley C Connection Project.

The preferred route for the new line – which will mainly follow the route of the existing 132,000-volt line on the western fringes of Nailsea – was announced by National Grid in September.

It said the new line would be mainly overground, but it would consider putting the cables underground “if the economies were right”.

The IPC ordered the independent report – published by the Institute of Engineering and Technology and consultants Parsons Brinckerhoff- after concerns that not all options for the newline had been properly investigated or costed.

The report agreed with National Grid that the cheapest option for the new power line was overhead cables, but it also put the costs of undergrounding the cables at between £10.2 million and £24.1 million a kilometre.

National Grid said the costs of underground cables would be 12-17 times more expensive than overhead lines, while the report reveals undergrounding would actually be four to six times more expensive.

Campaigners say National Grid needs to revisit the undergrounding option and look at burying all cables along the 37-mile proposed line.

Nailsea Action Against Pylons Action Group spokeswoman, Fiona Erleigh, said: “This report brings very good news. The report clearly shows that National Grid’s costs were out-of-date.

“At the initial public consultations on the Hinkley C Connection in autumn 2009, National Grid quoted underground cables to be 12-17 times more expensive than overhead lines.

“In this report, the relative lifetime costs show undergrounding being only four to six times more expensive. “This is a significant drop, making underground cables much more affordable.”

Campaigners calculate the cost implication to consumers of putting all of the Hinkley to Avonmouth route underground would cost consumers 30 pence annually per average household.

Mrs Erleigh added: “This is a trivial cost to preserve our landscape for future generations, to bury the blight of giant pylons and remove the fear of negative impacts on the health and homes of our communities in North Somerset.”

National Grid has until 2013 to submit its proposals to the Government and a final decision will be made by the IPC. The energy giant said it would be carefully studying the report over the next few weeks.