IT is "overwhelmingly likely" that Russian president Vladimir Putin ordered the use of a nerve agent in the attack on ex-spy Sergei Skripal in Britain, Foreign Secretary Boris Johnson has said.

Mr Johnson's decision to place blame for the attack in Salisbury on Mr Putin personally came as Britain awaited Moscow's response to the expulsion of 23 of its diplomats.

The foreign secretary's comments earned a scathing rebuke from Mr Putin's spokesman Dmitry Peskov, who said: "We have said on different levels and occasions that Russia has nothing to do with this story. Any reference or mentioning of our president is nothing else but shocking and unpardonable diplomatic misconduct."

The Kremlin is also considering its response to the United States after Donald Trump's administration imposed sanctions on Russians allegedly involved in interfering with the 2016 US elections and cyber-attacks.

Speaking at an event in Moscow on Thursday night, Vladimir Putin said Russia is a "proud" nation "and will be in the future, too".

Asked on Friday whether Moscow would expel UK diplomats, his foreign minister Sergei Lavrov said: "Of course we will."

Visiting the Battle of Britain Bunker museum in Uxbridge with his Polish counterpart, Mr Johnson singled out Mr Putin personally for blame.

"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, " said the Foreign Secretary.

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

Polish foreign minister Jacek Czaputowicz said: "We are sure that it is the Russian state which is involved in this attempt. It is certain."

Russia also gave a dismissive response to Defence Secretary Gavin Williamson's call for it to "go away and shut up".

Mr Lavrov said: "I guess he wants to go down in history with some bombastic statements ... Maybe he lacks education, I don't know."

A Downing Street spokesman would not be drawn on whether Theresa May endorsed Mr Williamson's comments, saying only: "The prime minister sent her own very clear message to Russia over the course of the week."

The Daily Telegraph reported that the nerve agent used in the attack could have been planted in Yulia Skripal's suitcase during a recent trip to Moscow.

The newspaper said senior intelligence sources believe an item of clothing, cosmetics or a gift could have been laced with the Novichok toxin.

Labour leader Jeremy Corbyn, whose response to the attack has led to criticism from some on his backbenches, said "the evidence points towards Russia" being responsible - but the possibility of gangsters being behind the attack rather than the Kremlin could not be excluded.

He warned Mrs May not to "rush way ahead of the evidence" - highlighting the way international crises such as the Iraq War had seen "clear thinking" overwhelmed by "emotion and hasty judgments".

Writing in the Guardian he warned against a "new Cold War" of "escalating arms spending, proxy conflicts across the globe and a McCarthyite intolerance of dissent".

Confirming Labour's support for Mrs May's actions, Mr Corbyn said: "We agree with the Government's action in relation to Russian diplomats."

But he added: "Measures to tackle the oligarchs and their loot would have a far greater impact on Russia's elite than limited tit-for-tat expulsions."

Mr Corbyn said that Mrs May was right on Monday to identify two possibilities for the source of the nerve agent - either Russia authorised the attack or had lost control of the Novichok substance.

"If the latter, a connection to Russian mafia-like groups that have been allowed to gain a toehold in Britain cannot be excluded," he said.