Chelsea owner Roman Abramovich wins High Court battle against Russian oligarch Boris Berezovsky

Mr Berezovsky, 66, had accused the 45-year-old billionaire businessman of blackmail, breach of trust and breach of contract.

He was seeking more than £3billion of damages from Mr Abramovich, who denied the allegations and denied that Mr Berezovsky was entitled to damages.

This morning Mrs Justice Gloster ruled in Mr Abramovich's favour after a four-month trial in London which started in October 2011 and ended in January this year.

The legal fight centred on deals done in Russia following the break-up of the Soviet Union two decades ago.

Announcing her decision, Mrs Justice Gloster said she found Mr Abramovich "to be a truthful, and on the whole reliable, witness".

Mr Berezovsky, who was in court for today's ruling, told the trial that Mr Abramovich had "intimidated" him into selling shares in Russian oil company Sibneft at a fraction of their value.

He also told the judge that Mr Abramovich had broken a promise made during a deal relating to a Russian aluminium company, but Mr Abramovich disputed the claims.

Mrs Justice Gloster said she dismissed Mr Berezovsky's claims both in relation to Sibneft and in relation to RusAl "in their entirety".

The court heard how both men "rose to enormous wealth and influence" in Russia in the 1990s as state-owned firms were privatised in the wake of the collapse of communism.

In 2000 Mr Berezovsky fled Russia after falling out with President Vladimir Putin. He settled in England, after initially going to France.

Mr Berezovsky claimed that he had been betrayed by his former friend and business partner, but Mr Abramovich said the claims were "wholly without merit".

During the trial, Laurence Rabinowitz QC, for Mr Berezovsky, said both men had worked together to acquire Sibneft, and became friends.

Mr Berezovsky claimed that in 1995 he, a colleague and Mr Abramovich agreed to "work together" to bring Sibneft under their control.

They had persuaded then Russian president Boris Yeltsin to "bring about the privatisation of Sibneft and its disposal into their hands", said Mr Rabinowitz.

But, said the QC, Mr Abramovich had intimidated Mr Berezovsky and his colleague into selling their ownership interest in Sibneft at a "massive undervalue" and put Mr Berezovsky "in fear for the life of his friend and the risk that his property might be expropriated".

Jonathan Sumption QC, for Mr Abramovich, said Mr Berezovsky was paid millions of pounds by businesses controlled by Mr Abramovich for his services as a "political godfather".

But Mr Sumption said Mr Berezovsky had not "contributed a single cent" to acquiring or building up Sibneft, nor made any managerial contribution.

He said Mr Berezovsky's contribution had been "important, indeed... indispensable" but "almost entirely political".