The Russian foreign ministry has given Britain one month to cut its entire diplomatic staff to match Russia’s own mission to the UK as the fallout following the Salisbury poisoning intensified.

The move could see scores of employees in the British embassy in Moscow and consulates in St Petersburg and Ekaterinburg dismissed from their jobs.

Laurie Bristow, Britain’s ambassador to Moscow, was summoned for talks and told to reduce staff at his embassy and the consulates to mirror the exact size of Russia’s diplomatic mission in the UK. Russia has an embassy in London and consulate in Edinburgh.

Although the Foreign Office refused to say whether this meant Russia was effectively increasing the number of diplomats it was expelling, a spokeswoman described the latest development as “regrettable” but “anticipated”.

The Russian ministry, in a statement, said it had summoned the British ambassador to the foreign ministry building and handed him a note of protest.

It said Britain's "provocative actions" had led to the decision by multiple Western governments to expel scores of Russian diplomats from their capitals.