A web of companies owned by an Iranian tycoon overcharged residents of an upmarket riverside development, a tribunal has revealed.

Charter Quay leaseholders are set to receive a £150,000 refund following the damning judgement by the Leasehold Valuation Tribunal (LVT).

The tribunal found many companies connected to the Kingston development in 2008 and 2009 were “owned or controlled by the Tchenguiz family”.

The business empire is headed by Vincent Tchenguiz, a Mayfair resident who is understood to have a 130ft motor yacht Veni Vidi Vici, which stands for “I came, I saw, I conquered”, on the French Riviera.

Vincent, who has a younger brother, Robert, left Iran after the 1979 revolution and chairs the Consensus Group which advises on an investment portfolio worth £4.5bn.

The tribunal found the companies traded with each other on financially favourable terms, to the detriment of leaseholders who faced excessive service charges or “onerous” costs to end contracts early.

Tribunal chairman Adrian Jack said: “It is astonishing that County Estate had no system in place to warn employees that if they were going to enter contracts with other Tchenguiz companies they needed to ensure that the terms were reasonable.”

Charter Quay residents first rebelled when they received a £5m estimate for future repairs in 2007, later reduced to £2.5m after they commissioned an independent surveyor.

In 2009 they won a case at the LVT to remove County Estate Management, a Tchenguiz company, as manager, and received a service charge refund after a later hearing.

Derek Winsor, 81, chairman of the residents’ association, said: “I came here with my wife 10 years ago hoping for a peaceful life, but we were absolutely astonished to see how the service charges started to creep up.

“We got a strong committee together of 12 people and we have attacked it with a strategy to go to the LVT.

“One of the positive effects is we are all talking to each other because we have all got a strong common interest.”

A Consensus spokesman said: “Estates and Management, on behalf of the head lease holder, is considering its options.

“To keep this award in perspective, the award was for only 18 per cent of the total sum claimed. Most costs were found to be completely reasonable.”

The tribunal laid bare the tactics used to squeeze money out of Charter Quay leaseholders.

The Tchenguiz company that managed the estate, County Estate, signed two 14-year contracts for intercom and CCTV with another Tchenguiz company, Interphone ltd, in 2007 and 2008.

County Estate’s property manager admitted she did not read, negotiate or seek alternatives to the contracts before signing them, but did not know Interphone was a Tchenguiz company.

The tribunal said: “The result of entering these contracts has been extremely damaging financially, because the break clauses are so onerous.”

A spokesman for Consensus said the contracts were renewed versions of earlier contacts signed before it owned Interphone.

Another Tchenguiz company that acted as landlord, Charter Quay Ltd, allowed yet another Tchenguiz company, Estate and Management, to charge a 23.5 per cent commission for commission for insurance.

The LVT ruling, delivered on Tuesday, November 22, branded the charge “excessive”, and said 10 per cent was the most that was reasonable.

Consensus said other LVTs have ruled 15 per cent and higher is a reasonable charge.

Tribunal chairman Adrian Jack also attacked County Estate’s “disgraceful” unco-operative behaviour after the tribunal removed it as manager in 2009.