The first major anti-terrorism exercise outside London took place in the drizzle of a crowded city centre today.

Police, paramedics and firecrews donned gasmasks and protective suits as screaming volunteers poured from Newcastle Civic Centre in a simulated terror attack.

The Health Protection Agency exercise - named Operation Magpie - was to test how well the emergency services and hospitals coped with a poison gas attack.

Hundreds of volunteers were evacuated from a conference room in the local government building, the target of the staged attack.

As walking 'survivors' were directed to inflatable decontamination tents, others were carried stretchers to waiting ambulances and driven to hospital.

Emergency services directors said it was important to see how well their plans worked for dealing with a terror strike, and how they could be improved.

Director of the HPA Emergency Response Division Dr Nigel Lightfoot said the simulation was the biggest field execise staged so far in the UK.

He said: "We are doing everything we can to make sure we are prepared for any emergency of this type, whether it results form a deliberate attack or a major accident.

"We need to test the resilience of the region in a situation such as this.

"The exercise is part of a programme of a programme of training exercises, and is the first to test the response of the health service in this way."

He stressed there was no specific threat to Newcastle.

Health Minister John Hutton arrived to witness the event.

He said: "Whatever an exercise like this costs, it is worth it.

"We need to make sure exactly how our emergency services will deal with a situation like this and this is the best way to do it.

"People should not be scared. But this is the world we live in today, and unfortunately an exercise such as this is necessary."

As firemen in flourescant sealed gas suits carried victims from the building, a group of 20 demonstrators dressed as Osama Bin Laden staged a rooftop protest against the proposed identity card scheme and the occupation of Iraq.

The Health Protection Agency works to protect health, prevent harm, and prepare for threats from infectious diseases, chemicals, poisons, and other radiological and environmental dangers.

North News, 69 Grainger Street, Newcastle upon Tyne, NE1 5JE.