A judge has warned sub-letting scams by crooks impersonating their landlords to trick unwary tenants out of deposits and rents are​ on the increase.

Jailing Heidi Korn for eight months after she was found guilty of fraud at Inner London Crown Court, Judge William Wood called for new measures – including landlords offering photographic proof of ownership – to curb what he called “an increasingly prevalent crime.

Korn had rented a £500,000 flat in Streatham Hill, London, for £1,600 a month and then tried to let the property for £1,800 a month to another tenant.

She was caught out when paperwork with a forged signature went astray and alerted the owners who reported Korn to police.

Korn had posed as the flat owner and forged tenancy agreements to trick the tenants into paying her an £1,800 deposit.

During the hearing, the judge ordered police to look into similar cases in Lambeth and Southwark, London.

Detectives uncovered 14 other offences during the previous five months. In some cases, the private rented homes were turned into brothels and drugs farms.

“Such crime must be deterred because it is all too easy to con landlords and results in serious harm to many people. It is grossly dishonest. It involves planning and prolonged deception of the victims,”

the judge said in court.

“There are multiple victims, both those who have a home to let and also those who believe that they are going to rent one.

“It is worth proposing that when a private landlord seeks references from a prospective tenant he or she should provide proof of ownership and photographic proof of identity.

“If this becomes the norm it will be much more difficult to commit this fraud.”

Korn had contacted the flat owners in a response to an advert offering the property to rent on web site Gumtree.

The court heard that the owners were owed £8,000 in lost rent due to the crime.