A Russian hit squad poisoned Sergei Skripal and his daughter by smearing nerve agent on his front door, police disclosed last night.

Counter-terrorism police revealed for the first time that they believed Colonel Skripal and his daughter Yulia "first came into contact" with the Novichok nerve agent at their home.

Scotland Yard added that the "highest concentration of the nerve agent" had been discovered on the front door of Col Skripal's home in a cul-de-sac close to Salisbury city centre.

Detective Sergeant Nick Bailey, who was also hospitalised, is thought to have become ill after going to the house and was one of the first on the scene.

The disclosure will intensify the manhunt for the would-be assassins who had targeted Col Skripal, 66, and his 33-year-old daughter. It will also heap further pressure on the Kremlin, which is accused of being behind the attack, for putting at risk anybody who had gone to the Skripals' home.