Alexei Navalny, the Russian opposition leader, has announced that he will run for office at the country’s next presidential elections in 2018.

The anti-corruption crusader is the first candidate to declare participation in a campaign which will almost certainly see him directly challenging Vladimir Putin for the keys to the Kremlin.

Mr Putin, who served two terms between 2000 and 2008 and returned to the presidency in 2012, has not yet said whether he will stand for a fourth term but is almost certain to do so.