Ministers are preparing to submit an extradition request to Moscow for two suspects responsible for the Salisbury nerve agent attack, as the Government vowed to exert "international pressure" to force Russia to "do the right thing".

Documents are being prepared to force the would-be assassins to return to the UK to face justice, although the order is not expected to be sent for a number of weeks or months.

Last night Government sources pledged to do everything possible to secure a conviction for the Skripal family after Sergei and his daughter Yulia were targeted in a nerve agent attack in March which prompted deep recriminations around the world.

Dawn Sturgess and Charlie Rowley were subsequently treated for exposure to the deadly nerve agent and Ms Sturgess died as a result.

The poison was smuggled into the UK and then dumped by the attackers, who British security services are sure were Russian nationals. More than 20 countries around the world expelled diplomats as a result.

Moscow is expected to reject any attempts to force its citizens back to the UK and last night confirmed it had not been sent a demand to do so. The Kremlin has launched a war of words after being accused of the crime, branding reports fake news.