The approval of a wind farm 13km off the Sussex coast has been met by opposition from conservation authorities.

The South Downs National Park (SDNPA), The National Trust and the Royal Society for the Protection of Birds (RSPB) have all expressed concern over E.ON’s 175-turbine Rampion wind farm, which was given consent by the Government last Wednesday.

The SDNPA said it would “scar” the county’s rare chalk grassland. The project means digging a 14km trench for an underground cable connection to the national grid running through the South Downs to a substation near Bolney.

Trevor Beattie, SDNPA chief executive, said: “There will be 14km of cable going straight through the rare chalk grassland of the national park.

“It is a rarer habitat than the Amazon rainforest.

“How long the scar will take to repair itself we don’t know.”

In the South Downs National Park, 4% of the land is chalk grassland.

The decision does mean E.ON has to pay the SDNPA £242,500 in mitigation and £116,000 for monitoring, while it has reduced the number of turbines from 195 to 175.

Mr Beattie welcomed the mitigation measures but felt they did not go far enough.

The National Trust is also disappointed by the level of mitigation.

Jane Cecil, the trust’s general manager for the South Downs, said: “We support renewable energy in principle but remain concerned about the major potential impact of the proposals on Birling Gap, Seven Sisters and the Heritage Coast.”

The RSPB is in favour of renewable energy but previously raised concerns about the wind farm’s impact on kittiwake breeding and birds migrating along the Channel, which could collide with the turbines.

However, not all environmentalists are against the wind farm. Brenda Pollack, from Friends of the Earth, described the approval as “fantastic”.

Michael Lewis, chief operating officer for E.ON Renewables, said: “We firmly believe Rampion will make a significant contribution towards meeting the UK’s renewable energy targets.”

Chris Tomlinson, development manager for Rampion Wind Farm, added: “The wind farm will not only help generate jobs but also provide a boost to the port regeneration at Newhaven and the local economy.”

E.ON said it would remain aware of the environmental impact of activities associated with building the wind farm.

The first sections of onshore cabling work are expected to start in spring 2015.

The farm is expected to produce enough energy to power two-thirds of the homes across Sussex.