Controversial basement conversions which have divided the Highgate community have been given the green light by Haringey Council – but will be subject to tighter planning rules.

A council meeting on Monday night (July 30) agreed that there are benefits to developing basements.

But applicants wanting to create exceptionally large excavations – known as type four basements – will now have to ensure hydrological and hydro-geological tests are carried out before any building work begins.

Residents have been worried about the risk of flooding, subsidence and contamination of ponds on Hampstead Heath as a result of subterranean excavations.

Despite agreeing the new guidelines, councillors passed a controversial planning application minutes later for a type four basement in Grange Road, Highgate, even though the surveys have not yet been carried out.

Carolyn Purves, who lives next door to the home where the basement is planned, said she was shocked by the decision.

“What is the point of the guidance notes when the first chance they have to follow it, they ignore it?” she asked. “They agreed this was a type four application and yet passed it without seeing the necessary reports.”

Howard Carter, the applicant, said he would make sure the surveys were carried out before building work took place.

“At the time we made this application, six to nine months ago, there was no guidance in terms of Haringey’s approach to basements,” he said.

“I have been always more than happy to accept the conditions and add to those conditions. They seem perfectly appropriate and if I were my neighbour I would be asking them the same things.”

But Professor Tony Wright, who has experienced four years of problems after a basement was dug near his Highgate home, warned of the dangers.

He said: “It has led to changes in the underground water distribution, so significant soil erosion has occurred.

“This has resulted in considerable damage to my property, but also the ground water is now bubbling up through the pavement at the front of my house.

“I personally don’t have a problem with basements as such, but the hydrodynamics of the area in which we live can have a significant effect and cause considerable distress to the local residents and even the builders themselves.”

Gail Waldman, of the Highgate Society, welcomed the tighter regulations but said the council must make sure it monitors building work.