Armed police will begin patrolling the streets of Sussex next week in preparation for the Labour Party conference.

Huge concrete and steel barriers to prevent car and truck bomb attacks are to be used to protect the conference site in Brighton.

An air exclusion zone will be in force and although police declined to reveal details, it is certain the RAF will have fighters ready to counter any aerial terror threat.

The tightest security measures ever seen will safeguard delegates as part of a £2.3 million operation to guard against terrorism.

More than 1,000 police officers will take part in Operation Otter, the largest of its kind undertaken by Sussex Police.

As in 2001, when Labour last visited the city two weeks after the September 11 terror attacks in America, the Brighton Centre and two nearby hotels will become a secure island site, sealed by fencing and concrete walls to prevent car bombings.

Armed police patrols will be increased before and during the conference, which takes place from September 26 to 30.

All 16,000 delegates and visitors have been vetted and will be searched each time they enter the island site.

Chief Superintendent Jeremy Paine, the officer in charge, said no specific terrorist threats against the conference had been received but the possibility of an attack remained in "everyone's minds".

He asked members of the public to be vigilant and report anything suspicious.

He said: "There is no information anyone is interested in targeting the conference.

"However, if something does become known, we will be ready for it.

"Brighton will be a very safe place to be during the conference."

The new pontoon-shaped barriers, made of steel encased in concrete, will be placed at any point around the island site where a car or truck attack could be possible.

The mobile 10ft by 3ft barriers, used with concrete wall sections, have been built for similar events elsewhere and were last seen at Labour's Manchester conference earlier in the year.

The Hilton Brighton Metropole hotel will once again be connected to the Grand and the Brighton Centre by a purpose-built bridge, which will cross Cannon Place. The adjacent Russell Road multi-storey car park will be shut and vehicles using the Churchill Square car parks will be searched.

Police will stop and search members of the public in the weeks before and during the conference and will be able to close all roads in the city at a moment's notice if a threat emerges.

Mr Paine said he would have at his disposal "all the necessary power" to cope with an attack from the air or from the sea.

The Home Office will foot the bill for security, which will allow at least two demonstrations or rallies, including one from Albion fans lobbying Deputy Prime Minister John Prescott to approve a new stadium at Falmer.

The second will be by the Trade Justice Movement, campaigning for worldwide fair trade.

Adam Bates, head of tourism at Brighton and Hove City Council, said the event injected £10 million to £15 million into the local economy, mainly for hotels, shops, businesses and taxis.