Giant overhead power lines could scar some of the 'most treasured landscapes' in Norfolk and Suffolk if they are built to take electricity from new offshore windfarms to the national grid, rural campaigners have warned.

The Country Land and Business Association (CLA) has urged local government minister Eric Pickles to press for power to be sent via underground cables rather than much cheaper pylons.

The CLA claims National Grid (NG) is planning to put a network of 'large scale' overhead lines across the countryside linking the offshore windfarms to London.

They claim there could be six so-called 'connection points' where the infrastructure has to be upgraded, including Norwich and Lowestoft.

NG revealed it can cost more than 10 times more for underground rather than overhead lines – and warned the bill would have to be passed on to customers.

The company said only 'exceptionally constrained' areas could be considered for underground cabling, but said the impact on the countryside was always taken in to account.

The CLA argues that 'outdated and outmoded research and development' are being used to calculate the cost and east regional director Nicola Currie said: 'We believe NG are looking at a number of places in Norfolk. NG's costings are based on a historic model of oil-filled cables and large cooling mechanisms which have essentially remained unchanged since the Fifties.'

Mrs Currie said more research had to be done into the alternative high voltage direct current (HVDC) transmission.

An NG spokesman said: 'When planning to connect a new generator to its network, National Grid considers different methods, including overhead lines, underground cables and subsea cables. We have to manage the costs of these projects responsibly as they will ultimately be paid for by electricity consumers. However, we also need to consider the impact on the local landscape and communities of what we build.'

She insisted cost comparisons were based on modern cables using plastic insulation, known as XLPE cables, not oil-filled cables.

'The costs of triple conductor overhead lines (where there are three wires suspended from each arm of the pylon, a total of 18 wires being carried by each pylon) are �1.8m per kilometre, while an equivalent set of buried underground cables would cost �22m per kilometre. The costs of twin conductor (where there are two wires suspended from each arm of the pylon, a total of 12 wires being carried by each pylon) would be �1.6m per kilometre, while an equivalent set of buried underground cables would cost �18m per kilometre.'

Mr Pickles has been urged by the CLA to confirm that he has asked NG to properly address research and development and to ensure that when he is asked to approve the proposals from the Infrastructure Planning Commission that NG will be asked if alternative offshore routes have been properly assessed using the latest technology.

Mrs Currie said she believed people would be prepared to pay 'a bit more' to ensure cables were put underground rather than overhead but added that NG should meet the cost.

NG is currently reviewing its approach to undergrounding and is asking the public, industry, government, environmental organisations and other bodies to have their say. People can find out more by going to www.nationalgridundergrounding.com