Boris Johnson has said the the Kremlin “must give answers” after an international watchdog confirmed that Sergei Skripal and his daughter Yulia were poisoned with a "high purity" strain of Novichok nerve agent in Salisbury.

The Organisation for the Prohibition of Chemical Weapons said that it had been able to “confirm” the findings of British scientists about the nerve agent.

It represents a significant boost to Theresa May, who has said that Russia was directly responsible for the attack. Mr Johnson said that only Russia has the “means, motive and record” to have carried out the attack.

He said: “We will now work tirelessly with our partners to help stamp out the grotesque use of weapons is this kind. The Kremlin must give answers. We must, as a world community, stand up for the rules based order which keeps us all safe. The use of weapons of this kind can never be justified, and must be ended.”

The OPCW conducted tests on blood samples from the Skripals and also an analysis on samples of the agent found in Salisbury.

The team also took samples from Detective Sergeant Nicholas Bailey, who was poisoned after coming into contact with the agent while assisting the Skripals.