Tenants of two buildings in east London have been awarded a six-figure sum in rent repayments by a tribunal after challenging a billionaire described by a judge as a “rogue landlord”.

The group of current and former residents of Olympic House and Simpson House in Hackney took companies owned by John Christodoulou to tribunal for operating unlicensed houses in multiple occupation (HMOs), which meant the buildings were not subject to the safety and quality standards required by law.

The London Renters Union, which represents the tenants’ group that brought the claim, said the lack of licensing left residents vulnerable to hazardous conditions, including fire risks due to inadequate safety measures.

Cyprus-born Christodoulou, 59, is based in Monaco and, according to the Sunday Times rich list last year, has an estimated wealth of £2.5bn. The Guardian has contacted his company Yianis Group for comment.

Jordan Osserman, a spokesperson for the campaign, said: “This case shows how the law is rigged against renters. Christodoulou makes millions off our rent while flouting the law and cutting corners on safety.”

During the hearing earlier in March, the judge in the first-tier tribunal (property chamber), Robert Latham, said: “The respondent can only be characterised as a rogue landlord.”

After a lengthy legal battle that began in 2020 – when the landlord rejected residents’ request for rent relief during the Covid-19 crisis, telling them they could use money saved on lunches to pay their rent in full – 46 residents from 15 different flats across Olympic House and Simpson House have been awarded a combined total of £263,555.68.

The ruling forms part of a rent repayment order (RRO). These were introduced in housing legislation in 2016 and empower the property chamber of the first-tier tribunal to force a landlord who has broken the law on housing standards to pay back part, or all, of the rent.

There are now concerns that Christodoulou may not pay, despite the order. The London Renters Union said the tenants had discovered that the landlord was attempting to liquidate the companies that the judgments are against after transferring ownership of Olympic House and Simpson House from one company to another within his corporate group at a large loss or undervalue.

Marc Sutton, a member of Somerford Grove Renters, which represents 170 flats in Olympic House, Simpson House and St John’s Court in Hackney, all majority-owned by Christodoulou, said: “This appears to be a deliberate attempt to evade financial responsibility through corporate restructuring.

“These tactics highlight how wealthy landlords manipulate corporate structures to avoid accountability while tenants suffer the consequences.”

Osserman added: “Even when we win in court, landlords like Christodoulou can game the system to avoid paying up.” He added: “The only way we can fight back is by organising and taking collective action.”