Police are 'confident' the conference will be able to go ahead

Although police said there was no indication of any specific threat, help is being sought from residents and businesses around the Brighton Centre.

A letter has been sent out saying people's "eyes and ears... are the most effective weapon against terrorism".

A secure "Island Site" will be in place around the conference centre from the evening of 23 September for six days.

It will also take in the Grand Hotel, the Metropole Hotel and exhibition halls, and the Russell Road NCP car park.

The conference runs from 25 to 29 September and Brighton and Hove City Council expects �10m to be injected into the local economy during and after the event.

Vehicle passes will be necessary for people who require access to the Island Site, as well as six streets immediately to the north of the sealed area.

Vehicle passes are available from the council and police Enlarge Map

They are: Russell Square, Clarence Square, Cannon Place, St Margaret's Place, Russell Mews and Russell Place.

Ch Insp Lawrence Hobbs, of Sussex Police, said: "We'll be doing everything we can to keep everyone safe and maintain business as usual for the city."

Police and the council have been communicating with around 1,000 residents and businesses who could be affected by Operation Otter.

A letter sent out in the wake of the London bomb attacks said that "hosting the government in Brighton during a time of international tension inevitably involves heightened security measures".

Local people are urged to be alert, but not alarmed.

Police want to know about suspect bags and packages, attempted credit card frauds, and any suspicious people looking to rent property or buy vehicles.