Following last week’s violent student protests, a large scale combined-force public order exercise has taken on a new importance, as  DAVID CLENSY reports.

AS an angry mob of students surges forward, and the "thin blue line" of police officers close ranks to counter the move, it's a scene that's unnervingly reminiscent of last week's ill-fated student demonstration in London – when a peaceful protest turned into "direct action" against the Tory HQ at Millbank.

Thankfully, the students swearing aggressively into the faces of the Avon and Somerset officers today are only acting.

The 170-strong force of "protestors" are actually students from the A-level course in public service, and they have come here to the US Air Force base at Fairford, Gloucestershire, to help officers train for public disorder scenarios.

These volunteers may be playing the roles of Islamic extremists or militant environmentalists during the two-day exercise, but there is no escaping the irony that it is students themselves who have caused police the greatest cause for concern in recent weeks.

"Don't worry, they're A-level students – they haven't had to take out a student loan just yet," jokes Inspector Steve McGrory, a specialist training officer who is organising the exercise, which has brought together more than 400 officers from all five of the South West's constabularies.

"Exercises like this are the best way to simulate large-scale crowd control, and to test our ability to provide a co-ordinated response as necessary.

"The operation will show the South West's five forces acting together, honing our ability to work as one in a live scenario."

The idea is to increase police power by occasionally merging the resources of the Avon and Somerset, Wiltshire, Dorset, Gloucestershire and Devon and Cornwall forces.

"With the sort of budget cuts we've seen in recent weeks, it's one way to ensure we have the manpower at our disposal to deal with a situation that could spiral into a serious public order incident," says Devon and Cornwall Deputy Chief Constable Paul Netherton – who is one of the "Gold Commanders", leading the mock-operations.

"We have large-scale public order exercises every three years, but this is the first time we've mixed up officers from all the different forces. We need to ensure our officers are able to be thrown together and work well as a team. It's all about getting the command and control structure working effectively.

"During the normal course of their duties, police officers are encouraged to work as individuals – we ask them to go out there and deal with incidents themselves and get to know members of their community on a one-to-one basis.

"But when it comes to dealing with a major public disturbance, such as a protest that descends into a riot, officers suddenly have to switch to working as a single unit.

"They have to start working in a more military manner – when the sergeant says do something, they simply have to do it."

The day starts with a briefing, in which the 400 officers are told the objective for the day: to allow the environmentalists' demo to go ahead smoothly – without crossing the line between democratic protest and illegal public disorder.

"It's all about giving a proportionate level of policing – allowing the democratic protest, but making it clear we won't allow the line to be crossed towards violent disorder," says Superintendent Mick Rogers, who, as "silver commander" at the exercise, is in charge of co-ordinating the way the police treat the protestors.

"After the student protests last week, we're very aware that the police are under extreme scrutiny. This exercise allows us to look at how we can adapt to the changing face of a protest as it evolves."

Outside on the airfield, the protest is noisily passing by, with the students being moved along by a walking pen made up of a couple of hundred officers.

"If things were to turn nasty, the officers would get closer together – literally closing ranks," Inspector Steve McGrory explains.

"Ultimately the riot gear would come out from the vans, and we could call in the police dogs and horses. But, generally, we prefer to maintain a friendlier face – the more aggressive we look, the more aggressive the protestors become."

As luck would have it, the exercise ends as it began – as a peaceful protest, with just one arrest made for public disorder.

"The point is, the officers never knew how the exercise would pan out," Inspector McGrory says. "And the fact is, most demonstrations end peacefully, just like this."