Mydeposits.co.uk, a government-approved tenancy deposit protection scheme, estimates there could be as many as 400,000 tenancies with unprotected deposits.

Even more worryingly, some tenants are still completely unaware tenancy deposit protection laws even exist.

Many only find out their landlord should have protected their deposit when things go wrong and they can’t get their money back.

With the average deposit protected being over £1,000, the losses can be significant.

Eddie Hooker, chief executive of mydeposits.co.uk, said: "These figures are concerning because if a deposit is never protected, the tenant has to rely on the landlord’s goodwill to have their cash returned.

"A protected deposit gives tenants the chance to raise a dispute at the end of the tenancy if they feel their landlord has unfairly withheld it. It also gives tenants access to free and impartial dispute resolution.

"Some tenants seem to be clueless about tenancy deposit protection. They need to be aware of what is happening with their money.

"You wouldn't just hand over £1,000 to a stranger without finding out what was going to happen to your money, why is a deposit any different? If in doubt ask your landlord or letting agent immediately."