By Barnie Choudhury BBC social affairs correspondent

Social Affairs Correspondent Barnie Choudhury looked at the growing problem for a new series of 'File on Four', which begins on Radio 4 at 2000 GMT on Tuesday.

In a city in the Midlands a man knocks hard on the window of the car in which my researcher and I are sitting.

You want that patch so you can make more money than anyone else Asian dealer

It has taken four weeks of careful negotiation to set up this meeting.

A series of telephone calls with contacts of untraceable contacts has brought us to this dimly lit alleyway.

I cannot see his face and I do not want to. He is wearing a baseball cap, a hooded track suit and jeans.

"Right," he says "here's the deal. You don't identify me. If I get caught and even if I'm in prison I'll hunt you down and kill you."

'Top dog'

He has been described to us as one of the biggest heroin dealers in the country.

All I know is that he is one of the growing number of dangerous Asian criminals bent on taking over Britain's heroin trade.

"There are only a few places where Asians haven't reached yet," he begins, "everybody gets edged out, you don't look at it as colour.

"You look at it as top dog and when you get to top dog you can edge anyone out."

Gun crime

It is not a boast. He says it in a tone that is matter of unchallengeable fact.

A quarter of UK heroin is said to have Pakistani links

He buys the heroin in bulk, �25,000 at a time from Bradford and makes at least �7,000 a week.

Drugs and gun crime go hand in hand.

He is protected and only four of the hundred in his organisation sell on the streets.

The rest are muscle to protect his dealers.

"Drugs culture is turf wars," he continues, "that's the way it is.

"You want that patch so you can make more money than anyone else. That's why you get so much gang warfare.

"Associates have had to use guns. I'm not saying I've had to use them 'cos I don't want to say I've had to use them, but there's a possibility I've had to use them."

Street dealers

There is no way of verifying this man's claims. But his account tallies with the investigation into drug crime and violence by Derbyshire Police.

The BBC's 'File on Four' investigation programme has been given exclusive access to their new weapon in the war against drugs.

We certainly see a significant involvement of Pakistani serious and organised criminals in both the importation and then the onward supply of heroin Donald Toon - Customs and Excise

The force uses available intelligence to build up complex maps - linking street dealers with suppliers wherever they are in the country. It is called 'mapping'.

Steve Holmes, who heads the mapping project, was an undercover drug squad detective for 13 years.

He is convinced Asian criminals are expanding their operations in heroin.

Mr Holmes said: "They've always been very organised. The change is they're organising each area.

"If you look at street dealing, local wholesalers and importers, they're involved in all areas rather than just the importation, and they've used the skills they've learnt in organising importations to organise other deals within England and within particular cities."

Heroin traffickers

Those cities includes Bradford, regarded by Steve Holmes as a main distribution hub for heroin.

"I think it's just family ties and they've made contact for local people and they've said 'if you want this come with me I'll introduce you, once you've got an area where you go to, you keep going there'."

According to the National Criminal Intelligence Service (NCIS) the amount seized from South Asian heroin traffickers has recently increased.

At best only two of the 30 tonnes entering Britain are ever stopped from hitting the streets.

'Organised criminals'

All communities have problems with drugs and this is not about demonising the Asian communities in Britain - 99.9% are law abiding.

But there is enough evidence to suggest a growing problem in drug crime in those particular communities.

Donald Toon, who is in charge of criminal investigation for Customs and Excise in the north of England, confirms the Asian link.

"We certainly see a significant involvement of Pakistani serious and organised criminals in both the importation and then the onward supply of heroin in the UK market," he said.

"The best estimate we have is that up to a quarter of heroin used in the UK may have some sort of Pakistani origin."

'Intelligence gap'

Once in the UK the dealers use their connections in large Asian areas - like Birmingham and Manchester - to distribute the heroin.

The Chief Constable of Greater Manchester, Mike Todd, says he is concerned that not enough is known about the Asian criminals.

"I think there's been a change with more drugs moving within the Asian community.

"That's why I have the grave concern for that at the moment and that's why we've got to fill that intelligence gap and we have to take those people out."

In Britain much of the attention in the war on drugs is focused on Yardies, Albanians and Turkish criminals.

But the evidence 'File On Four' has uncovered suggests that the authorities should examine drug crime and violence with in the Asian communities as a matter of urgency.