Billionaire declares his challenge to Putin for presidency

The billionaire’s decision comes after a tumultuous few weeks for Mr Putin, whose United Russia party barely scraped a majority in the elections held earlier this month, before tens of thousands of people held the largest anti-government protests that post-Soviet Russia has ever seen on Saturday, criticising electoral fraud and demanding an end to his rule.

Mr Prokhorov said: “I have made the most serious decision of my life. I am running for president.”

The businessman, who made much of his £11bn fortune in nickel and gold, said he would not build his presidential campaign on criticism of Mr Putin. “Criticism must make up no more than 10 per cent,” he said. “I would like to focus on the things I would do.”

Mr Prokhorov, who owns the US NBA New Jersey Nets basketball team, made a brief attempt to challenge the United Russia party at the parliamentary elections.

However he later resigned from his own party, the Right Cause party, following an internal power struggle that he blamed on the Kremlin.

The election saw United Russia lose a substantial share of its seats, although it retains a majority.

The independent Russian election-observer group Golos said the party “achieved the majority mandate by falsification”. International observers reported widespread irregularities.

The most dramatic of the protests saw a vast crowd jam an expansive Moscow square and adjacent streets. Police estimated the crowd at 30,000, although aerial photographs suggested up to 100,000.