Owners of large, empty detached houses in “Billionaires’ Row” have been urged to sell up following a spate of high-profile squatting cases in Hampstead Garden Suburb.

Squatters were caught last month trying to enter a derelict home in The Bishops Avenue, believed to be owned by the Saudi royal family.

Enormous homes in the exclusive road, which runs between Highgate and Hampstead Garden Suburb, are targets for squatters willing to brave high fences and 24-hour security, claim neighbours.

In December, Hampstead Garden Suburb Trust and Cllr John Marshall led calls for the Democratic Republic of Congo to put its �4million house in Holne Chase on the market after it fell victim to squatters.

A �10million mansion in Winnington Close linked to the Gaddafi family is also being occupied.

Frank Townsend, director of Savills in Hampstead, said London is an economic “safe haven” for overseas buyers.

But Dr Saul Zadka, who organised the storming of the Gaddafi house last year as a political statement, claims properties in the capital are bought by foreign buyers as places of refuge.

Dr Zadka, who is a trustee of the Suburb Trust, said: “While they keep these houses for a rainy day, they become a nuisance to the real people, of which the number is dwindling. It was a glamorous place not so long ago. The owners should be forced out or told they cannot leave it empty all the time.”

A security guard for security consultants Freeway Securities Limited said four mansions, believed to be owned by the Saudi royal family, had not been lived in for a few years.

The sprawling grounds have become overgrown after gardeners and landscapers were let go.

A pensioner, who has lived opposite a now-empty mansion in The Bishops Avenue for 45 years, said: “I am greatly concerned about the squatters because police can still say it’s a civil matter if someone complains. It should be illegal and it’s a bit of a worry that people could try their luck at my home if I go away on holiday.”

Finchley and Golders Green MP Mike Freer has campaigned for squatting to be criminalised and has worked on a bill to change squatters’ rights, which is being heard in the House of Lords.

He said: “Just because it’s a large house or owned by someone wealthy does not mean they should not have the same rights as everyone else not to have their house squatted.

“With squatting not being a criminal offence, neighbours worry about going on holiday and that’s not just the landlord or owner of the empty property but the neighbours as well. Squatting doesn’t bring empty houses back into use – it’s a complete red herring. Who should say if it should be occupied if someone buys a property and chooses not to live in it? We are in a property-owning democracy.”