A third Russian military intelligence officer who carried out a reconnaissance mission before the poisoning of Sergei Skripal has been identified by counter terrorism police and the security services, the Telegraph understands.

The GRU agent is believed to have visited Salisbury to help plan the attack before two of his colleagues brought weapons grade nerve agent into the UK.

It is understood that the man has now been identified by those investigating the planned hit in March, which inadvertently led to the death of local woman Dawn Sturgess.

It came as Jeremy Hunt, the Foreign Secretary, said he believed the Russians had made the attempt to kill the former spy because they felt they "got away" with the poisoning of Alexander Litvinenko in London in 2005.

"That's why Theresa May's reaction this time has been very different," Mr Hunt told Sky News.

He said the Kremlin would not have expected 28 countries around the world to expel more than 150 Russian diplomats.