Police have been catching criminals and preventing crimes for years by stopping and searching people on the street.

As one officer put it: "It is one of our best tools."

Recently-promoted Sgt Steve Curry, of Brighton police, realised its value while he was on foot patrol in the town's St James's Street last year.

He was speaking to a member of the public when he noticed a driver pull up sharply about 50 metres away.

The driver was acting suspiciously, pretending to clean his car with a hand-held vacuum cleaner.

Sgt Curry decided to investigate. As he was asking the driver about his out-of-date tax disc he noticed a meat cleaver on the back seat.

He waited for the right moment and then pounced, quickly handcuffing the driver and radioing for back-up.

Sgt Curry searched the man's clothes and in his jacket found a tiny white fragment, half the size of a fingernail. He also found another weapon, this time a knife. Sgt Brian Bell checked the boot and in the vacuum-cleaner box discovered a chunk of the same substance, the size of a fist.

Subsequent forensic tests showed it to be slate heroin, enough to raise more than £5,000 on the street.

This year, the driver was sentenced to six years for possession with intent and another year for possessing offensive weapons.

On the court steps before sentencing, the driver told an officer: "It was just a lucky day for you lot when you stopped me."

But there was no luck involved. Police are trained to be suspicious and to stop, search and investigate.

The problem in the past is that they have been accused of not having enough grounds to search people, something that has laid them open to accusations of racism.

As a report to the Sussex Police Authority pointed out: "There is evidence to show the disproportionate use of the stop-and-search power by police is used to the prejudice of visible ethnic minorities in general and African-Caribbean youth in particular.

"It has contributed to an erosion of their trust and confidence in policing."

There have been few such complaints in Sussex, but there is still a lack of trust in policing by some people from ethnic minorities.

The new policy is designed to build another bridge.

Until now, only full stops and searches were recorded, but it is a recommendation of the Stephen Lawrence inquiry that all "stops" should be written down as well, even if they do not result in a search.

Thorough recording means details can be checked if a complaint is made.

Equally important is that full reasons for the encounter are to be documented and given to the person stopped at the time.

This is designed to increase trust and confidence amongst ethnic minority communities by demonstrating the "fair and ethical" use of the tactics. In other words, to show they haven't been stopped just because they are from a visible ethnic minority.

Sussex Police has defined terminology for all officers: 'Stop' means when an officer requests a person to account for their actions, behaviour or possession of anything, whether the person is on foot or in a vehicle.

The key ingredient of the new policy is: "There should be no random or purposeless stopping of people. It should only take place on the premise that there is a pre-considered investigative reason. The grounds should be recorded."

Stop-and-search should only be carried out with "discretion and only after giving careful thought to the grounds for reasonable suspicion".

The emphasis is for officers to try to gain the co-operation of the person being searched.

All stops and searches, now termed 'street intervention', will involve the recording of a body map, showing where the person was searched, a description of the person, including details of ethnic background, vehicle searched, duration of stop and reasons.

The Sussex Police Authority approved the policy following a report from the authority's community liaison working party, chaired by Judith Corcho.

She commended the report and stressed her working party "understood the sensitivities surrounding stop-and-search, but recognised that it was an important policing tool".

A pilot project is being launched in Brighton later this year to shape and evaluate the policy with community assistance. A training package will be issued force-wide.

Chief Constable Paul Whitehouse said stops and searches in Sussex were low, but he hoped the number would now increase.

He said: "We are optimistic that spelling out this new policy to our officers will increase the numbers because it will give people more confidence to use this power."