A historic site in Highgate has been demolished and another in Fortune Green irreparably damaged - sparking calls for developers to be prosecuted.

Developers could face hefty fines after playing fast and loose with planning laws as they bulldozed a locally listed house and destroyed an artist’s historic studio window.

Planning officials are investigating both incidents.

Highgate Cllr Rachel Allison described the demolition of a ground floor extension of Goldsmiths Cottage in Denewood Road, Highgate, as the “the worst infringement of planning law” she had ever seen.

Residents were equally horrified when builders set to work smashing panes of glass and removing wooden frames from artist Isaac Snowman’s studio window in Ranulf Road, Fortune Green.

Cllr Allison called on Haringey Council to prosecute developers for the “shocking breach” in Highgate and warned other cases could follow if it went unpunished.

Only a small part of the former historic outbuilding in the heart of the Highgate conservation area is left.

Cllr Allison said: “You walk past and it is a case of - now you see it, now you don’t. How they had the gall to go in and demolish it completely? It is unbelievable.

“The more I think about it the more extraordinary it is.”

But architects insist the demolition does not overstep planning permission.

The cottage’s owners applied to demolish the cottage in 2006, but this was refused by the council and the Planning Inspectorate who both said it would harm the conservation area.

Last year the owners won permission to create a basement, extend the ground and first floors, and alter the roof.

Kennedy O’Callaghan, the architect who designed the renovation of the Highgate house, said: “We have permission for a basement and then a two storey building. It was only the single storey building that we had an obligation to retain.”

Work at the Snowman house in Fortune Green, which was built by the English artist who died in 1947, also angered residents.

The window of his studio has been classed as an “undesignated heritage asset”.

Bernard Heymann, of Ranulf Road, said: “I’m just pretty angry about the way people say bugger the law.

“They have smashed six or seven window panes and it’s like someone is putting up two fingers to the council.”

Camden Council rejected a planning application in March to renew permission to remodel the historic house.

Camden planning officials said: “The proposal would involve the loss of the studio window, which is integral to its local interest, the council will resist its loss.”

A council spokeswoman said the incident is being treated “seriously” and the owner will be encouraged to reinstate the window.