RIOTERS in the region are throwing so many petrol bombs at the police that their supply of empty milk bottles is dwindling fast.

The shocking admission was borne out yesterday as bricks rained down on lines of police as another officer was engulfed by the flames of a petrol bomb - for the third time in an hour.

A masked rioter picked his way through the crowd towards a shopping trolley, conveniently piled high with missiles.

"Excuse me," he says politely to the assembled crowd, "would you mind stepping back a little," then picks up a handful of bricks to continue pelting police lines.

Missile-throwing mobs are not normally so polite, but this is no ordinary mob - this is Durham Police's new £1m riot training school.

A disused plastics factory on Durham City's Meadowfield Industrial Estate has been converted into a centre to train police in a variety of public order situations, believed the best outside London.

Since it opened six months ago, it has trained 2,000 officers from the Durham and Cleveland forces in riot techniques, and instructors hope to interest forces from around the country as well as other agencies such as Customs and Excise.

Lanchester Dairy is currently providing a supply of reject milk bottles for use as petrol bombs, but with up to 100 a day going off, it is unable to keep up with demand.

A Durham force spokesman said: "Supply is struggling to meet demand and it will soon be necessary to look for extra pintas."

Officers are put through their paces at the public order training centre - dealing with an outbreak of disorder in the confined spaces of a simulated prison wing, breaking down the armoured doors favoured by drug dealers and controlling the crowds in the aftermath of a terrorist attack in a city street.

The most dramatic exercise is the simulated riot training, where a squad of about 20 officers come under attack.

Instructors pull no punches - wooden bricks batter the officers' riot shields and the air reeks of petrol from the dozens of bombs thrown at the front rank - but realism is everything.

During the skirmishing, a petrol bomb set fire to PC Terry France, the third time in less than an hour the officer had been engulfed in flames.

He said: "It looks a lot worse than it actually is."

The centre also offers an unusual advertising opportunity - staff are looking for businesses to sponsor shopfronts and garage forecourts to make the streets as realistic as possible.

And of course, anyone with a large supply of unwanted milk bottles.