Russia is sending fishing trawlers to track and spy on the UK ’s critical network of undersea cables , a new analysis has suggested.

Ministers said Vladimir Putin is using “commercial proxies” as part of his espionage strategy to map the exact locations of the cables , which link the UK with the US and Europe , in case of conflict. Any sabotage to the network risks huge disruption to banks, hospitals, mobile phone networks, and other vital services.

An analysis published on Thursday by The Telegraph found more than 500 incidents of Russian trawlers loitering over the lines, or following them for miles, have been recorded.

It comes as the government prepares to crack down on those who damage cables, proposing lengthy jail terms and unlimited fines as punishment.

A Nato source told the newspaper: “We’re absolutely aware of what Russian civilian fishing ships are up to and where ...…