Jonathan Davidson, of Broudie Jackson Canter solicitors, said the Purplebricks blunder would cost landlords currently trying to evict tenants another £5,000 on top of the fines for inadequate deposit documentation.

He said: “Landlords will face extra bills if their eviction proceedings collapse, particularly if they have to cover tenants’ legal bills. It will easily cost £5,000 and, at the end of it, the tenant will still be in the property.”

Giles Peaker, of Anthony Gold solicitors, said the courts would likely find in favour of the tenant for any ongoing eviction. He added: “Tenants now have a very effective defence. The deposit information can be provided late, but it has to be provided before a Section 21 is served. If it hasn’t, the eviction should fail.”

Chris Norris, of the National Residential Landlords Association, a landlord body, said it would take Purplebricks landlords another six months to correct the paperwork and re-evict their tenants. He added that it was likely landlords using Section 21 were either trying to sell their properties and leave the market or evict tenants for anti-social behaviour.

Mr Davidson said any Purplebricks tenants who had recently been evicted also potentially had legal grounds to have the Section 21 overturned. However the lawyer said any tenant wrongfully evicted in the past had no rights to move back into the property or claim any additional costs other than the deposit fines.

 A Purplebricks spokesman said: “As soon as we became aware of this issue, we immediately stopped serving new Section 21 notices. We will be reissuing updated prescribed information so that new Section 21 procedures can commence.”

The issue also only applies to Section 21 “no-fault” eviction notices. Evictions made under Section 8 will still be valid.