Security plans for the Labour Party's autumn conference were left in a hotel bar in Manchester, it has emerged.
A member of Midland Hotel staff misplaced the document
Greater Manchester Police (GMP) said the force was handed the documents by a local newspaper after they were found in the city centre Midland Hotel.
A police spokesman said the documents did not contain secret information, and would not compromise security at the September conference at G-Mex.
A Labour Party spokesman said it did not comment on security issues.
GMP said that the dossier, which was left in a public area of the Midland Hotel, had been misplaced by a member of the hotel's staff.
A police spokeswoman said: "The information it contains was not secret and GMP is happy to share it with partner agencies. It does not compromise the security operation surrounding the conference.
The conference is due to be held at G-Mex in September
"Policing the Labour Party conference is a major security operation and it is recognised good practice to share information and involve partner agencies in the planning of an event of this scale.
"We will be discussing future working arrangements with other agencies in light of this recent incident.
"Greater Manchester Police take all information and intelligence about security issues extremely seriously.
"There is no intelligence to suggest that this event is a specific target for terrorists.
"However we are conscious of the fact that the city has been targeted in the past so we need to remain vigilant and it is only right that we have contingency plans in place to deal with all manner of eventualities."
She added: "Officers are confident that the folder does not belong to a member of GMP staff and are currently talking to partners to establish how the file was misplaced."