Chestertons has apologised after a letter sent out by one of its branches to a member of the public included a copy of much of its database containing hundreds of names.

At least one of the names is a famous one.

The firm said it should never have happened, but it was an isolated incident.

The letter was sent to a vendor who had withdrawn their instruction.

The letter, from the branch in Chiswick, west London, warned the sellers of the possibility of being liable for dual agency fees should “one of these applicants have purchased your property or subsequently purchase your property within six months”.

Attached to the letter was a list of names running to over eight pages, together with the dates that each had been sent information about the property. No contact details were included.

The agent now marketing the property said he had been shocked to have been shown the letter by the clients.

He said: “Effectively, what they had done was email the property to a large section of their database, that this counted as an introduction, and they wanted a fee if one of those named went on to buy the property.

“I was shocked when I saw the letter coming from such a reputable agent.”

He said the letter also raised concerns about data protection.

However, Robert Sturges, Chestertons’ area director, said: “This was an isolated incident and the result of human error.

“We are very sorry and hope to have the opportunity to apologise to our former clients.”