Russian dissident Boris Berezovsky, who was one of Vladimir Putin's fiercest critics, has been found dead at his home in the UK.

The circumstances of the death of the tycoon and former Kremlin insider were unclear. However, initial reports said he had taken his own life and was found in his bath.

A spokesman for his company, Bell Pottinger, said Berezovsky was found at his home in Ascot, Berkshire.

Berezovsky, 67, had survived several assassination attempts, including a bomb in Moscow that decapitated his chauffeur in 1994.

He had been a wanted man in Russia since 2001, charged with fraud and political corruption. Berezovsky had previously spoken of fears for his safety, saying that Putin was prepared to kill anyone he deemed an enemy of Russia and that he was a target.

The oligarch and former mathematics professor, who made his fortune importing Mercedes-Benz cars into Russia in the 1990s, was part of Boris Yeltsin's inner circle in the latter years of his presidency, and became deputy secretary of Russia's security council.

He played a role in Putin's initial rise to power but subsequently became dedicated to the anti-Putin cause. He left Russia for self-imposed exile in the UK at the end of 2000.

Berezovsky was not afraid of provoking the wrath of the Kremlin. In 2007 he openly spoke of plans to plot the violent overthrow of Putin and claimed he was bankrolling people close to the president who were conspiring to mount a palace coup.

"We need to use force to change this regime," he said. "It isn't possible to change this regime through democratic means.

"There can be no change without force, pressure."

The exiled businessman was also a close associate of Alexander Litvinenko, the Russian spy and dissident who was fatally poisoned with radioactive polonium-210 in London in 2006.

Berezovsky helped Litvinenko publicise claims that Putin organised the bombings of apartment blocks in Russia in 1999, which paved the way for Russia's second military intervention in Chechnya.

In recent years, Berezovsky's wealth is thought to have considerably diminished, with a series of court cases leaving him with hefty legal bills. Last year he lost a legal battle with Chelsea FC owner Roman Abramovich, a former associate who he fell out with as Putin came to power.

Berezovsky had lodged a claim for damages of around £3 billion, claiming Abramovich had intimidated him into selling shares in Russian oil giant Sibneft for a "fraction of their true worth". However, the London Commercial Court judge said Berezovsky had been an "inherently unreliable" witness.

His former partner, Yelena Gorbunova, had also been involved in a legal battle with Berezovsky, claiming she was owed around £5 million from the proceeds of sale of a property in Surrey.

Last week it was reported that Berezovsky had been forced to try to sell a limited edition Andy Warhol print of the former Soviet leader Vladimir Lenin as part of attempts to pay off creditors and legal bills, which have also included putting his classic 1927 Rolls-Royce up for sale and offloading several homes.