Detectives tracking the movements of Russian spy Sergei Skripal and daughter Yulia say that their mobile phones were turned off for four hours on the day they were poisoned.

The devices’ GPS signals which identify positions were not in operation during a crucial period in which their movements remain unknown, according to the Sun

It suggests that the pair were trying to meet someone “off the record” before they were attacked with the nerve agent Novichok.

Sputnik news reports: This may mean they were poisoned after switching off their phones to keep a clandestine meeting secret.

“The most likely reason would be if they were going to meet someone and wanted to remain off the radar. This would fit with the tradecraft Skripal used as a spy,” The Sun on Sunday quoted an unnamed source as saying.

A Scotland Yard spokeswoman refused to discuss any details when meeting with reporters on Sunday.

According to the information which has so far been made available to the public, at 9:19 a.m. on March 4 Sergei Skripal and his daughter Yulia visited the graves of Skripal’s wife and son in a local cemetery in Salisbury.

At 1:30 p.m. they parked their car and dropped by a local pub. Shortly after that they dined at a restaurant.

According to the Times, mobile providers have informed police about the Skripals’ phone communications on the day of the attack.

On March 4, Sergei Skripal and his daughter were poisoned with what the British authorities say was a nerve agent, dubbed A-234, allegedly developed in Russia