Thieves have stolen a laptop containing top secret security plans for next week's Labour Party conference.
Security plans have been "fully reviewed"
The computer was taken from a car driven by a member of the armed forces when it was parked at motorway services on the M3 in Hampshire on Tuesday.
The laptop also contained security plans for next month's Conservative party conference in Dorset.
An MoD spokesman said security plans for the conferences in Manchester and Bournemouth had been "fully reviewed".
'Security not compromised'
The laptop and a satellite navigation system were stolen from the car at 0930 BST on Tuesday from the Fleet Service Station.
The MoD spokesman said: "We can confirm that an incident has taken place which is being investigated by the police.
"In the light of this security arrangements for the conferences are being fully reviewed and internal procedures re-examined."
A spokesman for Greater Manchester Police said plans for policing the conference, which starts on Sunday at the city's GMEX conference centre, had been changed to ensure security was not compromised.
He said: "We would like to reassure the public that GMP's priority is to ensure that the conference and those attending it are safe and secure and we have implemented a robust policing operation to achieve this, while causing minimum disruption to the public."