The world’s biggest accountancy firm helped in falsifying documents to hide Roman Abramovich’s wealth and evade tax, BBC Panorama has found.

Accounts signed off by Deloitte in Cyprus meant assets such as superyachts, mansions and private jets worth $672m (£508m) vanished from Abramovich’s company accounts.

Deloitte also appears to have advised on a scheme to evade a huge tax bill on the oligarch’s wealth through the falsification of documents.

Barrister Andrew Mitchell KC, an expert in financial services law, said Panorama’s evidence showed the scheme was “straightforward” tax evasion and “it couldn’t be more blatant”.

Roman Abramovich’s lawyers said he denies that he evaded tax or concealed his fortune. They said Panorama provided no evidence he knew about, authorised or directed the falsification of any document and said it was legitimate to rely on advice from professionals.

Deloitte Cyprus said it “acts in compliance with applicable laws”.

The findings are being revealed following a joint investigation between BBC Panorama and the Bureau of Investigative Journalism.

For nearly two decades, Roman Abramovich was the most famous Russian oligarch in the UK, welcomed in London where he bought Chelsea Football Club in 2003 and bankrolled the club’s most successful period. But after Russia’s full-scale invasion of Ukraine in 2022, he was sanctioned by the UK government as an associate of President Vladimir Putin and forced to sell the club.

Abramovich has been reported to be living in Turkey, a safe haven for him because it did not apply sanctions. In the Channel Island of Jersey, £5.4bn of his assets remain frozen and a criminal investigation has been going on for four years.

The oligarch’s lawyers told the BBC he denies the allegations in the Jersey investigation and says it was “undertaken for political purposes”.

Our investigation has uncovered new evidence about the way Abramovich’s business empire has been run. It also raises serious questions about the integrity of some of his professional advisers.