Buildings put up without planning permission are turning the borough into a “shanty town”, according to neighbours.
The unauthorised developments have begun cropping up in the area over the past five years, prompting concerned homeowners to speak up against the issue.
Denis Robb, of Victoria Road, New Barnet, has spent years trying to bring the problem to the attention of Barnet Borough Council.
In one letter seen by the Times Series, a planning enforcement officer admits one building does breach planning regulations - but the violation does not justify any action.
Mr Robb, 61, said: “It’s wrecking the area for future generations. When you walk around here, it looks like a shanty town.
“People don’t want to see the quality of the area they live in go down, but that’s what’s happening at the moment. It’s degrading. My neighbours and I are very angry about it.”
The issue has arisen in other London boroughs, and there is a major new government programme to tear down illegal properties in West London.
Market researcher Mr Robb says the majority of the new builds in Barnet are disguised as garden sheds - but are in fact bungalows or two stories high.
He added: “It’s left me baffled - what does constitute a legal dwelling and why are penalties not being enforced? I’d love to know.
“The buildings are ugly, vaguely industrial. They’re everywhere and I’ve got no idea what they are being used for.
“It doesn’t show respect for neighbours and that’s wrong. It’s totally selfish.”
A statement from Barnet Borough Council said: “Where planning regulations are breached, the council will always act accordingly.
“We are currently looking into the situation in New Barnet and if it is found that regulations have been breached, the owners will be asked to remove the structure entirely, make alterations to ensure it falls within permitted development rights, or seek planning permission for its retention.
"Should none of those actions be taken, the council can consider serving a planning enforcement notice, which would require demolition of the structure.”