Sergei Skripal and his daughter Yulia turned off the GPS tracking on their mobile telephones for four hours on the day they were poisoned by a nerve agent, The Sun on Sunday reported.
The devices' GPS signals which identify positions were not in operation during a crucial period in which their movements remain unknown, the newspaper wrote.
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.
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.
The pair remains in critical, but stable condition in a Salisbury District Hospital.
Prime Minister Theresa May was quick to blame Moscow for the attack and expelled 23 Russian diplomats. Moscow responded by sending home a similar number of British diplomats.
President Putin has said that it is “nonsense and absurd to claim that Russia would do anything like that before the elections and the World Cup.”
He emphasized that Russia had destroyed all its stockpiles of military-grade chemicals under the watchful eyes of international observers. Putin also said that Russia is open to working with London to investigate the poisoning, provided the UK is willing, which is not the case at the moment.
READ MORE: Who Could Benefit From Poisoning Former Spy Sergei Skripal