Campaigners opposed to the multimillion-pound project by Transco to pump gas from a new liquified natural gas (LNG) terminal in South Wales to Gloucestershire have called on the Prince of Wales to block the scheme by refusing access to land owned by his Duchy of Cornwall estate.
Transco, which is responsible for maintaining Britain's gas infrastructure, argues that the 180-mile pipeline from Milford Haven to the Tewkesbury area is needed to meet the UK's booming gas needs as it moves from a net natural gas exporter to an importer.
But opponents of the scheme claim its likely route, to be announced within the next fortnight, will take it through protected land, including the Brecon Beacons National Park and sensitive sites along the rivers Towy, Usk and Wye.
Conservationists are concerned that the pipeline will also go through Turnastone Court, a 247-acre farm in Herefordshire's Golden Valley, which features unique water meadows unploughed for 400 years. The farm was saved from ruin five years ago by the Countryside Restoration Trust (CRT) after an unspecified donation by Prince Charles.
Robin Page, chairman of the CRT, said yesterday: "This is a pipeline that will pass through some of the last unspoilt areas of Britain, when the same infrastructure is already in place on the other side of the country. In order to build this pipeline, ancient grazing land would be dissected, the water table and the hydrology of Britain's most ancient water meadows would be threatened, and some of Britain's most threatened flora and fauna would be compromised. It is almost beyond belief."
Turnastone Court is also the site of 16th- and 17th-century earthworks that form part of some of Britain's oldest irrigation works designed to create the water meadows, which are home to dozens of species.
Transco insisted last night that the final pipeline route, consisting of a one kilometre-wide corridor which will be narrowed down to a 44-metre-wide (144ft) excavation site after consultations with land owners, has yet to be decided. The pipeline will be 1.2m in diameter and buried 1.2m under ground.
But The Independent has learnt that the proposed route will cut across a 33-mile section of the Brecon Beacons and cross the territory of 420 landowners at a cost of £4,000 per acre in compensation.
Campaigners are hoping to stop the pipeline - being built in two stages from Milford Haven to Aberdulais, near Swansea, and then to Tirley, near Tewkesbury - by persuading landowners to refuse to sell.
Mr Page said: "We are asking neighbouring farmers for support. We want Prince Charles to know exactly what is going on. He is one of the few people to understand what is happening in the countryside today. We hope the Duchy will take a stand against the pipeline, wherever it goes."
The Duchy of Cornwall said yesterday that it was awaiting publication of the Transco plans. But sources said the proposals were expected to affect only three fields owned by the estate.
A Transco spokesman said: "We fully appreciate the sensitivities that a project such as this creates and when the route has been decided we will discuss it in detail with those affected."