Greedy go-betweens acting for high net worth individuals and film stars are demanding so much money for their services that deals are falling through.

In one recent case, one fixer for an American A-lister wanted 20% of the rent of a prime property. This was on top of any agent charges – and even the mega rich can’t, or won’t, pay.

The matter has become a big talking point among agents in easily the smallest – but also easily the priciest – property market in the UK: prime central London.

Property finder Simon Barnes, of H. Barnes & Co, said: “Last week we lost two substantial deals because of unrealistic, bordering on ridiculous, fee demands by clients’ advisers.”

He said that ‘fixers’ have long been a feature of the prime central London property market, accepted by both buying and sales agents.

He said: “Agents recognise and wholly accept that there will be people acting as intermediaries/advisers/runners, who will introduce buyers and basically ‘need looking after’ (paying).

“Sellers also recognise this and usually account for this in their fee structures.

“However, more recently the number of requests and the amounts expected, in fact demanded, has risen dramatically.

“It has reached such an unrealistic level that it is preventing deals being done.

“On two occasions in the past week, one with a high ranking Middle Eastern Royal and one high profile American, neither got properties they  wanted, despite offering acceptable prices.

“The sole reason was that their advisers’ fee demands could not be met.

“In other cases, greedy intermediaries want only ‘off market’ properties, so there is no website evidence of the price.

“They have then inflated prices in the hope their clients will pay more and they can pocket the difference.

“Yet this rarely works as sooner or later the real asking price is revealed and the deal collapses – assuming it ever gets agreed at all.”