Developers must clarify whether dumping mud from near Hinkley Point nuclear plant is covered by an environmental impact assessment (EIA), a judge has said this week.

Judge Milwyn Jarman said EDF’s evidence was “not accurate on a very important point” on whether material dredged from the seabed at Hinkley Point C site near Burnham-On-Sea was included in the EIA.

Campaigners want an injunction to halt the dumping that began last week, but a High Court hearing in Cardiff was adjourned on Monday for seven days.

About 300,000 tonnes is to be dredged from the seabed near the building site and deposited in the Cardiff Grounds, a mile off the coast of the Welsh capital.

EDF, which is behind the £19.6bn plan to build the nuclear plant, argues the mud dump was addressed in a main environment statement that formed part of the main planning application for Hinkley Point C and was approved by the UK Government.

But the judge said that was not clear from a witness statement the company had submitted to court. The firm’s barrister James McClelland accepted the wording could have been made clearer.

Legal action is being brought by the Campaign Against Hinkley Mud Dumping.

Campaigners asked for a temporary injunction to be imposed until the next hearing, but the request was turned down.

Campaigners are reportedly planning to organise a blockade with boats in an effort to halt the dumping.

A barge made its first trip to dump mud last week despite thousands of people protesting against the plan.