Protesters have occupied the construction site in the Swansea Valley Enlarge Image

They moved onto the National Grid construction site in Pontardawe in the Swansea Valley, on Monday and crawled inside the pipeline.

Work has stopped on that section of the pipe - which is to carry gas from two liquefied natural gas (LNG) terminals.

The campaigners said they will remain there as long as is possible.

When finished the pipeline will stretch 150 miles from south west Wales and through the Brecon Beacons into Gloucestershire.

It will supply a fifth of Britain's gas.

I'm sure we've got a lot more willpower than someone who doesn't really care and they're just here to be paid Protester Nick

The protesters claim the pipeline is causing significant damage and the want the project abandoned. They are also calling for ecologically-friendly sources of energy to be used, instead of fossil fuel ones.

Protester Jim Dunkley from the Safe Haven Network said; "We will fight this every step of the way and I will emphasise we will fight this non-violently.

"We are not here to cause trouble, We're here because we're concerned about the environment.

"We're here because we're concerned about safety - there are safety issue with this pipeline.

Jim Dunckley said they were staging a peaceful protest

"We're here because we're concerned about the future and the world our children will grow up in."

Some of those living nearby the construction site have offered protesters food after they were allowed on to the site by the landowner Eira Wyn Jones.

Mrs Jones said: "I think they've got a perfect right to show their protests and I've allowed them on the fields. I would presume that most farmers would let them."

One protester, identified only as Nick, described the conditions inside the pipe.

"You can kind of walk down it but very crouched over. It's normally best to slide down it, because it's downhill, down the mountain and then try and walk back up it on your knees.

Asked how long they were prepared to stay, Nick said: "Well, we're very determined people, and if it's a case of willpower, I'm sure we've got a lot more willpower than someone who doesn't really care and they're just here to be paid - to pay their mortgage - so longer than them"

National Grid said this particular section of the pipeline received ministerial consent a year ago.

'Safety and welfare'

The company said it wants to work with people, not against them.

National Grid's Paul Crumpston said: "This project is vital for securing the UK's energy needs for the future. We've worked very hard with the local community to explain exactly what we're doing.

"But construction sites are dangerous places and we're very concerned for the safety and welfare of the people who are currently on the site."

Police are remaining at the scene "to maintain the peace of the protest and to ensure the health and safety of all concerned," a spokesman said.