Former Russian spy Sergei Skripal and his daughter Yulia were saved from death because the deadly nerve agent smeared on their front door was 'washed off by the rain'.

The double agent, 66 and his daughter, 33, were left in a critical condition in hospital after being poisoned by Novichok in Salisbury on March 4.

The wide-scale operation investigated dozens of different ways the pair could have been infected by the nerve agent, from the restaurant they went to, to flowers left on their relatives' graves.

But after detectives came to the conclusion the pair were poisoned at Mr Skripal's home it has now been claimed the poison didn't work properly because of damp conditions.

Ex-Russian scientist Vil Mirzayanov says the hitman who carried out the attack failed to kill their victims because the Novichok was 'washed off the door handle'.

Ex-Russian scientist Vil Mirzayanov says the hitman who carried out the attack on Sergei and Yulia Skripal in Salisbury failed to kill their victims because the Novichok was 'washed off the door handle' of the former double agent's home (pictured)

Victims: Sergei Skripal, 66 and Yulia, 33 were left critical in hospital after the attack in March

He told The Sun: 'The substance was used when it was quite foggy — water droplets were in the air. It can be used only in dry air.

'In such weather conditions this substance could be used only by an idiot who knows nothing about the chemical characteristics of Novichok.

'If you drop it into water in some hours no trace will be left. It dissolves in water.'

Prime Minister Theresa May has formerly accused Moscow of carrying out the near-fatal assault, but they have repeatedly denied it.

Yulia Skripal has now left hospital and is being kept under police guard at a secret location.

Her father is still in hospital, but is believed to be improving.

It has now been claimed the poison didn't work properly because of damp conditions

The revelation comes after hackers posted a cryptic post on Miss Skripal's social media accounts.

A link was posted on Yulia Skripal's account to a well-known Russian song entitled Don't Lose Heart from a popular Soviet-era children's film, on March 7.

The posting was made three days after the Salisbury attack – when Miss Skripal, 33, pictured, was heavily sedated in hospital – leading to suspicions her account may have been hacked.

Poignant lyrics include: 'Did it happen by the will of fate, or is it due to our nature? Why do we for heaven's sake have so many enemies?'

The discovery comes after British intelligence revealed that Russian agents hacked Miss Skripal's emails for at least five years before she and her father were poisoned.