Why would a picture of a Mini Cooper stuck in a muddy field make so many people around London chuckle when it popped into their e-mail inboxes?

Because it is a Foxtons-liveried Mini and the estate agent is probably the most derided in its field - witness members of a website devoted to criticising Foxtons.

As will the anarchists from Class War who yesterday announced plans to picket the Foxtons branch in Islington - which looks more like a nightclub than an estate agents - claiming that its staff are driving up property values.

Foxtons is known for taking a bigger commission to sell your house than almost any other agent - 2.5 per cent, against an average of 1.5 per cent - which it justifies by promising to squeeze from a buyer the highest possible price.

However, it is not just about Foxtons's commission and the supposed effect on house prices.

A BBC investigation in 2006 saw Anna Adams, a reporter, pose as a Foxtons staff member for three months. She described “young agents in Foxtons exchanging high-fives as they swap tales of gazumping and over-valuing”. She also alleged incidents of faked signatures, and a close relationship between Foxtons agents and some independent mortgage brokers.

“They openly discuss potential buyers' budgets so they can squeeze as much money out of them as possible,” Adams said. A Foxtons spokeswoman said that these were “isolated, and distorted, incidents” but experts said that the brand had been tarnished.

Robert Jones, a brand consultant for Wolff Olins, said: “They are the masters of the Mini and their store design is innovative but they are all about image and this no longer washes with the much more informed customer of today.

“In the last five years the big brands are successful because of their functionality, such as eBay. Foxtons look glitzy but are a dinosaur. They also lack generosity.”

Foxtons said: “Like any estate agent, we receive criticism. We do believe, however, that we get it right the vast majority of the time, which is why we receive so much repeat business.”

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