Russia says Boris Johnson's claim Putin ordered nerve agent attack on spy is 'unforgivable'

Response marks rapid escalation in rhetoric between London and Moscow, amid growing fears of a looming cold war

The Kremlin has issued a furious response to Boris Johnson's claim that Vladimir Putin ordered the nerve agent attack on a former Russian spy in Salisbury, labelling it a "unforgivable breach of diplomatic etiquette".

Britain's Foreign Secretary had asserted it was “overwhelmingly likely” that it was the Russian President's decision to have Sergei Skripal poisoned.

And Moscow wasted little time in rejecting the latest "shocking" statement from a senior member of the UK Government, which itself marked an escalation in the hostile rhetoric being exchanged by the two countries.

Presidential press-secretary Dmitry Peskov told the state-run Tass news agency: “We have already said on many levels that Russia has nothing to do with this story whatsoever.

"Any reference or mention of our president in this connection is nothing but a shocking and unforgivable violation of the diplomatic rules of propriety."

Speaking during a visit to the Battle of Britain Bunker museum in Uxbridge, with his Polish counterpart, Jacek Czaputowicz, Mr Johnson had said: "Our quarrel is with Putin's Kremlin, and with his decision - and we think it overwhelmingly likely that it was his decision - to direct the use of a nerve agent on the streets of the UK, on the streets of Europe, for the first time since the Second World War.

"That is why we are at odds with Russia."

Russian foreign minister Sergey Lavrov had previously insisted Moscow had "stopped paying attention" to British statements about the poisoning.

He also criticised Gavin Williamson after the Defence Secretary suggestion on Thursday that Russia should "go away and shut up".

"Maybe he lacks education," Mr Lavrov said.

Theresa May announced a series of measures targeting Russia on Wednesday.

A total of 23 Russian diplomats will be expelled from the UK, while suspected spies will be detained at the country's border, checks on private flights will be increased and some Russian state assets will be frozen.

The assassination attempt on Mr Skripal on 4 March left the 66-year-old and his daughter, Yulia, in a critical condition in hospital.