A controversial pipeline being built across south Wales to Gloucestershire is facing a further setback.
The pipeline will eventually supply 20% of the UK's energy
A High Court judge has struck down a decision to grant planning permission for a terminus being built in Cilfrew, near Neath, as "unlawful".
The construction of the pipe to transport liquefied natural gas (LNG) from Milford Haven has already been disrupted by environmental protesters.
The 190-mile (306km) pipe will provide 20% of the UK's energy supply.
The scheme to build the terminus at Cilfrew was given the green light by the planning committee of Neath Port Talbot County Borough Council in September last year by a 13-12 majority.
A protest was staged inside the pipeline in Trebanos last November
But London's High Court heard that four councillors from the Ratepayers Party had been told not to take part in the planning decision on whether it should be built above the ground.
Council officials advised them not to vote because they had attended an earlier protest meeting against the plans.
The four were also told if they did vote it could lead to complaints to an ombudsman or legal challenge.
The councillors adopted a neutral stance and did not go on a site visit.
When the plan was approved, residents who believed the situation to be unfair sought a judicial review.
They were concerned about increased traffic and a potential environmental hazard because of old mine workings in the area.
On Friday, the judge struck down the decision made by the local authority's planning committee last September as "unlawful" and ordered the vote be taken again.
High Court Judge Mr Justice Collins said the councillors should never been told not to vote.
He said: "The councillors did feel under pressure not to participate. Where it seems that the advice given was clearly wrong, was in raising the threat of a complaint to the ombudsman."
He went on to say that councillors should not be inhibited from "doing the duty imposed upon them by the democratic system by the over-cautious advice from monitoring observers".
All four councillors - none of whom have indicated which way they would vote - could take part in the new decision, he said.
He also gave permission for the National Grid, the contractors building the pipeline, to maintain the site where work has already begun but further development is now suspended.
Protests have already been held against the construction of the pipeline which will link LNG terminals in Milford Haven to the national network in Swansea and ultimately Gloucestershire.
As well as a protest at the South Hook LNG terminal near Milford Haven last month, work on the pipeline at Trebanos in the Swansea Valley was halted in November by demonstrators who climbed inside the pipe.
A statement from Neath Port Talbot Council said: "We will now have to carefully consider the court judgement before being able to give consideration to the now undetermined planning application and the next course of action."
National Grid also said they were reviewing the judge's decision.