Pressure is growing to renegotiate or leave an international convention blamed for slowing building projects and increasing costs after a judge warned campaigners they are in danger of “the misuse of judicial review”.

Under the Aarhus Convention, campaigners who challenge projects on environmental grounds but then lose in court against housing and big infrastructure have their costs above £10,000 capped and the rest met by the taxpayer.

Government figures say this situation is “mad” but ministers have not acted, despite promising to do so for months.

The Tories are today leading the call for change with a demand to reform or leave the convention.

In March, Sky News revealed how a computer scientist from Norfolk had challenged a carbon capture and storage project attached to a gas-fired power station on multiple occasions.

Andrew Boswell took his challenge all the way the appeal court, causing delays of months at a cost of over £100m to the developers.

In May, the verdict handed down by the Court of Appeal was scathing about Dr Boswell’s case.

“Dr Boswell’s approach is, we think, a classic example of the misuse of judicial review in order to continue a campaign against a development… once a party has lost the argument on the planning merits,” wrote the judges.

They added: “Such an approach is inimical to the scheme enacted by parliament for the taking of decisions in the public interest,” adding his case “betrays a serious misunderstanding of the decision of the Supreme Court” and “the appeal must therefore be rejected”.

Another case – against a housing development in a series of fields in Cranbrook, Kent – was thrown out by judges in recent weeks.

The case was brought by CPRE Kent, the countryside challenge, to preserve a set of fields between two housing developments alongside an area of outstanding natural beauty.

John Wotton, from CPRE Kent, suggested it would have been hard to bring the challenge without the costs being capped.

“We would’ve had to think very carefully about whether we could impose that financial risk on the charity,” he told Sky News.

After his case was dismissed, Berkeley Homes said the situation was “clearly absurd and highlights how incredibly slow and uncertain our regulatory system has become”.

They added: “We welcome the government’s commitment to tackle the blockages which stop businesses from investing and frustrate the delivery of much needed homes, jobs and growth.

“We need to make the current system work properly so that homes can actually get built instead of being tied-up in bureaucracy by any individual or organisation who wants to stop them against the will of the government.”

‘Reform could breach international law’

Around 80 cases a year are brought under the Aarhus Convention, Sky News has learned.

The way Britain interprets Aarhus is unique as a result of the UK’s distinctive legal system and the loser pays principle.

Barrister Nick Grant, a planning and environment expert who has represented government and campaigns, said the convention means more legally adventurous claims.

“What you might end up doing is bringing a claim on more adventurous grounds, additional grounds, running points – feeling comfortable running points – that you might not have otherwise run.

“So it’s both people bringing claims, but also how they bring the claims, and what points they run. This cap facilitates it basically.”

However, Mr Grant said that it would be difficult to reform: “Fundamentally, the convention is doing what it was designed to do, which is to facilitate access to justice.

“And it then becomes a question for the policymakers as to what effect is this having and do we want to maintain that? It will be difficult for us to reform it internally without being in breach of our international law obligations”

In March, Sky News was told Number 10 is actively looking at the convention.

Multiple figures in government have said the situation with Britain’s participation in the Aarhus Convention is “mad” but Sky News understands nothing of significance is coming on this subject.

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The Tories, however, want action.

Robert Jenrick, shadow justice secretary and former housing minister, said the Tories would reform or leave the convention.

He told Sky News: “I think the country faces a choice. Do we want to get the economy firing on all cylinders or not?

“We’ve got to reform the planning system and we’ve got to ensure that judicial review… is not used to gum up the system and this convention is clearly one of the issues that has to be addressed.

“We either reform it, if that’s possible. I’m very sceptical because accords like this are very challenging and it takes many many years to reform them.

“If that isn’t possible, then we absolutely should think about leaving because what we’ve got to do is put the interest of the British public first.”

Mr Jenrick also attacked the lawyers who work on Aarhus cases on behalf of clients.

“A cottage industry has grown. In fact, it’s bigger than a cottage industry,” he said.

“There are activist lawyers with campaign groups who are now, frankly, profiteering from this convention. And it is costing the British taxpayer a vast amount of money. These lawyers are getting richer. The country is getting poorer.”