Aides to Russian billionaire Roman Abramovich, including staff at the accountancy firm Deloitte in Cyprus, appear to have falsified paperwork to hide his assets and avoid tax, according to leaked records reviewed by the BBC and The Guardian.

The BBC's Panorama program found that accounts signed off by Deloitte Cyprus made superyachts, mansions and private jets worth $672 million disappear from Abramovich's company accounts. Deloitte also appears to have advised on a plan to avoid a large tax bill by falsifying documents, the BBC reported.

"It couldn't be more blatant," barrister Andrew Mitchell told the BBC. He called the scheme "straightforward" tax evasion.

The Guardian says the records show a long-running effort to backdate papers from 1999 until at least 2013. The goal, it says, was to make deals look as if they had happened years earlier. Abramovich's closest aide, London-based Eugene Tenenbaum, appears to have been involved and may have given false evidence to a UK court, the papers suggest.

The findings come from the Cyprus Confidential leak, more than 500,000 documents shared with journalists. The BBC worked with the Bureau of Investigative Journalism.

Abramovich's lawyers say he did not evade tax or hide his fortune. They say he relied on advice from professionals. Tenenbaum also denies wrongdoing. Deloitte Cyprus says it "acts in compliance with all applicable laws."

Abramovich made his fortune from Siberian oil fields after the Soviet Union fell. He bought Chelsea Football Club in 2003. After Russia's full invasion of Ukraine in 2022, Britain sanctioned him as an associate of Vladimir Putin and he was forced to sell the club.

What we know: Leaked records appear to show backdated documents that helped hide Abramovich's assets, and he and Deloitte deny breaking the law.
What we don't: Whether tax authorities in Britain or elsewhere will open cases, and how much tax may be owed.