James Blitz

Vladimir Putin takes part in a judo training session in December 2009 (ALEXEY DRUZHININ/AFP/Getty Images)

Vladimir Putin’s visit to London on Thursday is probably the most remarkable diplomatic moment of this Olympic fortnight. Mr Putin is not coming to the UK on an official visit – he’s here in a private capacity to watch Olympics judo. But this is the first time he has been in London for a bilateral visit since 2003, when he was still viewed positively by some in the west and was accorded a state visit by Tony Blair’s government. An awful lot has changed since then and hence it is a moment to watch.

Ever since the 2006 murder in London of Alexander Litvinenko, the former KGB agent, relations between London and Moscow have been very frosty. Britain’s security services have long taken the view that the murder was carried out at the behest of the Russian state, and the brutality of the killing – by means of polonium poisoning – has never been completely eradicated from British minds. As a result, there has been only one visit by a British prime minister to Russia in the six years since then (by David Cameron in 2011). All other meetings with Russian leaders have been at international summits.