A police officer is in intensive care after being poisoned by a nerve agent when he came to the aid of the Russian spy targeted in Salisbury.

The unnamed officer was one of the first on the scene on Sunday when Sergei Skripal and his daughter, Yulia, were attacked by would-be assassins at a shopping arcade in the city centre.

The policeman was initially treated in hospital as a precaution and then discharged, but his condition deteriorated and he was readmitted on Tuesday and taken into intensive care.

On Thursday morning, Amber Rudd, the Home Secretary, disclosed on ITV's Good Morning Britain that the officer is "talking" in hospital so she is "more optimistic for him", but said the "targets" remain in a serious condition.

The disclosure of the officer’s condition will add to growing pressure on the Government to take a hardline approach against Russia if state involvement is confirmed.

Boris Johnson, the Foreign Secretary, described the events as “very troubling”. He said: “If this does turn out to be in any way the result of hostile activity by another government, or directed, led, by another government, then the people of this country can be absolutely sure that the UK will respond robustly.”