Boris Berezovsky, the high-profile Russian oligarch who became a vociferous critic of the Kremlin from his new base in Britain, died today.

A close friend confirmed to The Telegraph that Mr Berezovsky died at his estate in Surrey. The circumstances of the death remain unknown but the 67 year-old businessman is thought to have been found dead in his bath. It will inevitably raise questions about nefarious activities because Mr Berezovsky had survived several assassination attempts, including a bomb that decapitated his chauffeur. He was also a close friend of Alexander Litvinenko, the Russian dissident who was fatally poisoned with radioactive polonium-210 in London in 2006. Another close friend in the "London Circle" of exiled but influential Russians is Ahkmed Zakayev, who was also the subject of a plot to assassinate him on British soil.

British police have launched an investigation into the death of Boris Berezovsky. The businessman was found dead in his bath in Ascot, Berkshire, according to the latest unofficial information.

There is no evidence so far that a "third party" was involved in the death of Boris Berezovsky, police say.

Earlier, the Russian tycoon's house in Berkshire was given the all-clear after it was searched by police for chemical, biological and nuclear material.

His body remained at the property while the search - described by police as a precaution - for chemical, biological, radiological and nuclear material was carried out.

The search was sparked after a paramedic's personal electronic dosimeter (PED) - a health and safety device - was triggered.