It’s a scary thought that thousands of ghost buy to let tenants live in secret behind closed doors away from the prying eyes of property investors.

For around half of all the country’s letting agents claim to have rumbled these ghost tenants while passing homes they manage or calling round for property inspections.

Landlord insurance firm Direct Line for Business did a quick calculation and figured out around 3 million ghost tenants are freeloading in someone else’s private rented home.

When quizzed by letting agents, these tenants claim they have lived in the home for at least six months.

Many of these ghost tenants are live-in lovers who stay over long term because renting and running one home is cheaper than paying for two.

Others are friends who out stay their invites or tenants who the main tenant is sub-letting to for a price.

Having these shadow tenants ghosting about in private rented homes can cause all sorts of legal problems for landlords.

Not only will their presence void any landlord insurance, explains Direct Line for Business, but possibly the buildings cover as well. Many lenders stipulate borrowers must have valid buildings insurance or they are considered in breach of the mortgage contract.

Then the issue is the number of people living in a home. In some council areas, homes shared by more than three unrelated adult tenants need a licence, while homes with more than five tenants must have a council licence by law.

Direct Line for Business gave one example of a two bedroomed terraced house in Reading that had several families living there – but only name was on the tenancy agreement.

Jane Guaschi, of Direct Line for Business, said: “Lettings agents have seen significant damage from people crammed into a home who are not listed on the lease. In one property we heard of, shelving had been removed from a cupboard under the stairs to create a makeshift bedroom.”