The pipeline route runs behind Liz Whomsley's back garden

The National Grid strongly disputed the claim. It said it held an exhibition and structural tests would be done on nearby homes before blasting.

Test explosions were to take place in Trebanos on Tuesday but were delayed.

Opponents of the pipe linking two liquefied natural gas (LNG) plants with England said they had safety concerns.

Explosive charges will be used to create the route for the pipe, which will carry pressurised natural gas as it passes under a former quarry in Trebanos.

The test blasting is only the start - there are huge ones to come Liz Whomsley

Liz Whomsley, whose garden borders the quarry, said: "My main concern is the pipeline is too close to areas of population.

"I feel that the safety aspect of this huge pipeline has not been investigated enough yet.

"It's really difficult to get information but I've been able to find out that they were planning on doing some test blasting this afternoon.

"Apparently they would sound off a siren first but I have not been told how many (explosions) there were going to be and when I asked if other people in this vicinity had been told I was told no.

"It's a really alarming situation. The test blasting is only the start - there are huge ones to come.

Linda Ware of Safe Haven wants the project called in

"They are going down 30 metres underneath the road and underneath the river."

She was being supported by the Safe Haven Network, which has called on the Welsh Assembly Government to call in the project.

Campaigners delivered leaflets outlining their concerns door to door in Trebanos on Tuesday.

Spokeswoman Linda Ware called it the "biggest infrastructure project in Wales for at least 25 years" but said its members were unable to get answers.

A National Grid spokeswoman said it staged an exhibition giving details of its plans, including the need to tunnel, at the leisure centre in Trebanos on 6 June.

She said the test blasting, which would last less than hour, had been delayed because a key member of its team could not be present, but said it would go ahead in the next few weeks.