The government is investigating claims that a document outlining the prime minister’s schedule for a visit to Cheshire was left on a train.
According to the Mirror, the briefing note was found on the floor of a first-class carriage on a train heading from Manchester to Edinburgh in January.
The document identified details such as a private address where Theresa May was attending a dinner that evening.
A Cabinet Office spokeswoman said they had been made aware of the claims.
The two-page briefing note was found by a member of the public at around midday on the day of the trip, the Mirror said.
‘Serious security breach’
It detailed Mrs May’s plans for the day when she visited north-west England for a regional cabinet meeting.
The document identified the hotel where the prime minister had planned to spend several hours working on papers and making phone calls.
A government spokesman said: “We have been made aware of claims around a government document and will investigate accordingly.”
A former royal bodyguard, Inspector Ken Wharfe, told the Mirror it was a serious security breach.
He said: “In today’s environment, it becomes a serious security matter when documents like this detailing the hourly movements of a protected person are misplaced. That’s just not acceptable.”