Fraud investigators have launched a crackdown on a luxury housing block off Edgware Road in a bid to halt illegal sub-letting plaguing north Westminster.

Four people have been arrested and many more interviewed over the past few weeks after investigators visited 16 properties at the 600-flat Park West development.

The illegal practice sees tenants earn thousands of pounds a year from sub-letting their properties while, in many cases, they are fraudulently claiming housing benefit.

A three-bedroom council house in Westminster costs an average of just over �100 a week but a tenant can make as much as �750 a week from illegal sub-letting.

As well as Park West, where up to 100 flats are believed to be illegally sub-let, Westminster Council officers have targeted Dudley Court in Upper Berkeley Street and Carlton Gate in Maida Vale.

The council’s finance boss Cllr Philippa Roe said: “Westminster has some of the most desirable property in the country – due in part to its location.

“Combined with the amount of housing benefit currently available and the capital’s transient population, illegally sub-letting property is unfortunately rather lucrative. But we hope our efforts to crack down on fraud and the forthcoming cap will lead to a dramatic decline.”

It is believed many of those taking up short-term tenancies in Westminster are from Middle Eastern countries including some who come to England for medical treatment.

The recent crackdown follows a campaign by the council’s fraud team in 2008, which focused on benefit cheats sub-letting their Park West properties to Kuwaiti medical tourists.

Younis Ali, 43, was given a four-month curfew and ordered to pay �1,300 for claiming housing benefit for his Park West property while he sub-let the flat to tenants and lived with his wife on the Warwick Estate in Little Venice.

Earlier this year, Tatiana Piovezana, 30, was sentenced to 150 hours’ community service after admitting receiving more than �20,000 in housing benefits for a Carlton Gate flat she no longer lived in.

The council estimates five to 10 per cent of tenants are sub-letting their properties at any one time.

Hyde Park Cllr Heather Acton says that councillors in her ward and Bryanston and Dorset Square ward have allocated funds from their ward budgets to address the issue.

“We seem to have had more complaints recently so I suspect the problem is increasing,” she said. “It’s a problem for all sorts of practical reasons, aside from the illegality.”