Why are we asking this now?

Boris Berezovsky is a Russian multi-millionaire living in exile in Britain. An assiduous self-publicist and ferocious critic of President Putin, he is once again basking in the limelight after telling a newspaper that he was fomenting a revolution to oust the Russian president.

The immediate response of the Russian authorities was to lodge a formal complaint with the British government, via their ambassador in London, demanding that Berezovsky's political asylum status be revoked. This was swiftly followed by a letter from Russia's general prosecutor to the Home Office and an arrest warrant, charging that Berezovsky had called for the overthrow of Russia's legitimate government by force. Any delay in acting on this, the Russian ambassador warned, could affect bilateral relations.

Who is Berezovsky, really?

Berezovsky is the archetypal, perhaps even the original, Russian oligarch. Now 61, he made his money in the Russian economic chaos of the late Eighties and early Nineties as the Soviet union was falling apart. He skipped from the used-car sector, where he made his first million - private cars being in extremely short supply in Soviet times - into oil and then into media ownership. At each stage he showed an uncanny sense of "the next big thing" and an acute awareness of the political context. Critics would say that he was a wheeler- dealer of the first order, who was not particularly scrupulous about the ends for which he used his undoubted personal charm.

Was he always destined for fame and fortune?

Absolutely not. He was born into a blue-collar family in Moscow and had to overcome all the obstacles the Soviet system placed in the path of Jewish students with ambitions. Rather than computer studies at the prestigious Moscow University, he had to settle for maths and engineering at the forestry institute, after which he followed an uneventful academic career. By then in his forties, he was a classic beneficiary of times that favoured the fittest, most fortunate and most ruthless. His estimated wealth now is at around £800m.

How did he fetch up in Britain?

Berezovsky's financial interests in television brought him almost inevitably into politics. He entered the inner circle of Boris Yeltsin in the mid-Nineties, and helped to bankroll his campaign for re-election in 1996, as well as placing his television channels at his disposal. Yeltsin won, despite lagging far behind the Communist Party's candidate at the outset.

Berezovsky was rewarded with membership of Yeltsin's National Security Council. He was found a safe seat and entered the Russian parliament in 1999. Relations with the Yeltsin group cooled, though, and he found himself competing for presidential attention with Vladimir Putin, with whom he crossed swords in two crucial areas: over Putin's re-launch of the Chechen war in 1999-2000 (Berezovsky had been Russia's chief negotiator with Chechnya), and over his decision to revisit the way the oligarchs had made their fortunes. When the Russian authorities brought charges against him for tax evasion and embezzlement the following year, he fled to London.

Why wasn't this the end of it?

For three main reasons. First, because Berezovsky's name in Russia had become a byword for all the dubious ways in which a few canny individuals had enriched themselves in the Nineties; he was - and is - widely regarded there as a thief of the people's wealth on the grand scale. Second, because Putin bears personal grudges and sees Berezovsky as an arch-foe. And third, because Berezovsky felt the same way and has used his perch in London to campaign quite openly against Putin's presidency. Until recently, he also retained shares in a Russian newspaper, Kommersant.

How does he spend his time in Britain?

He has an office in Mayfair, lives with his third wife on a country estate, runs a fleet of armoured limousines and retains a PR agency to represent him. He manages his large property interests - which is where much of his money is now invested - and has become adept at schmoozing the great and the good of his country of exile.

The rest of his time appears to be spent in the company of like-minded Russian dissidents - rich and poor, resident here or passing through. The extent of his influence within Russia or the international diaspora, however, is hard to gauge, even though much of his time seems to be spent plotting.

He was certainly associated with the abortive presidential bid by Ivan Rybkin in 2004, which fizzled out early in very strange circumstances. He also claimed to have funded the Orange Revolution in Ukraine, but this always sounded like bravado. There is speculation now that Gary Kasparov's opposition grouping The Other Russia may be among the beneficiaries of the financial support Berezovsky says he gives to opponents of President Putin. Berezovsky is careful not to name the recipients of his largesse, however.

What was all that about Berezovsky and Litvinenko?

It is known that Berezovsky was supporting the former Russian spy Alexander Litvinenko financially. According to some reports, Litvinenko had refused an order from the Russian secret service to assassinate Berezovsky, who felt in his debt as a result. Litvinenko apparently fled to Britain immediately afterwards.

Amid the wilder speculation that followed Litvinenko's death of polonium-210 poisoning in London last year was a claim that Berezovsky had ordered his killing in order to put Putin in the frame. It was rapidly discounted. The killer, or killers, of Litvinenko have still not been brought to justice.

Could Berezovsky be extradited?

It is possible, but extremely unlikely. The precise reasons why someone is granted asylum are treated as confidential, and the Home Office has always declined to explain why Berezovsky was granted asylum in 2003. But it is thought that it was because his lawyers convinced the British authorities that he would not get a fair trial in Russia and that his life would be in danger - the Litvinenko connection again - if he returned.

Berezovsky's bottomless pockets may also have been a consideration. Berezovsky could hire the best lawyers in the business and go from appeal to appeal. Recognising that they were likely to lose in the end, the British granted asylum without any fuss. The same arguments would certainly be advanced in any extradition proceedings, and the result - as the Russian authorities seem tacitly to acknowledge - would be the same. Berezovsky might qualify to be sent back, but it is highly unlikely that any British court would deliver him over to Russian justice.