Theresa May is expected to announce sanctions against Russia as soon as Monday as pressure mounted on her to take “meaningful” action against Vladimir Putin over the Salisbury poisoning case.

The Prime Minister is expecting to receive confirmation from the Ministry of Defence’s Porton Down laboratory over the weekend that Russia was, beyond reasonable doubt, the source of the nerve agent used in the attempted murder of former double agent Sergei Skripal and his daughter Yulia.

Amber Rudd, the Home Secretary, will chair a meeting of the Government’s Cobra emergency committee on Saturday, the first time it will have met on a Saturday since last year’s Manchester suicide bombing.

Downing Street sources said the decision to call a Cobra meeting for 1pm reflected the “fast moving pace” of the investigation as police and the security services close in on the “who, what, when” of the poisoning.

Mrs May will spend this weekend at home in her Maidenhead Constituency contemplating the Government’s response to last Sunday’s attack, which also left Det Serg Nick Bailey in hospital after he visited Mr Skripal’s house.