A source last week said that if everyone eligible to do so claimed money, the liabilities could be in the region of £30m. 

The Telegraph understands that the mistake – an error in basic tenancy law – dates 2012 and tenants have a six-year limitation period in which to make a claim against either an agent or their landlord.

Purplebricks said: “The company recently became aware of a process issue in how it has been communicating with tenants on behalf of its landlords in relation to deposit registrations. 

“Further enquiries into this matter are currently being conducted and the communications process is now being corrected.”

Purplebricks, which was founded in 2012 and floated on Aim in 2015, was heavily loss-making until April this year, when it reported its first full-year pre-tax profit of £3.6m, on sales of £90.9m.

It had £58m of cash on the balance sheet in October, which means it should be able to absorb any claims “comfortably”, according to analysts at Peel Hunt, who have put their rating on the shares under review.

The company has had a tough time in the past few months as it deals with a number of separate problems.

Purplebricks has faced claims it failed to register tenant deposits with a government-approved protection scheme, blaming an IT glitch for the error.

The company is also disputing accusations from estate agents who believe they are entitled to holiday pay and pensions contributions from Purplebricks, despite being classed as self-employed by the company. Last month it issued a profit warning after business dropped.

Its share price has tumbled by 95pc over the past four years and the stock is now worth just a quarter of its float price of 100p.

Deloitte declined to comment.