Police and Department of Trade investigators say criminals are moving on to the airwaves to circumvent police action to block the illegal pay parties.
Figures to be published next week will show an increase in pirate radio activity.
Radio investigation officers who track down pirate transmitters are understood to have encountered unprecedented levels of violence.
A threat was made to throw one team from the roof of a block of flats, while others raiding stations have been targeted with blocks of concrete from high-rise buildings.
By using pirate stations, the organisers can broadcast hours of popular dance music which in many cases is not played by more staid legal stations. After it has attracted an underground audience, the station begins announcing details of the illegal rave, the venue of which is disclosed at the last minute. Once the plans have been revealed, the station packs up and moves on. Other pirate stations are believed to organise legal parties in clubs, providing a ready market in which associates can supply drugs.
'It is illegal to advertise an unlawful pay party, so the respectable radio stations won't broadcast details,' said Detective Chief Inspector Alan Burrell, head of the former Midlands pay party intelligence unit - it was disbanded in May.
'Pirate radio stations are now being seen as a way to pass information to all and sundry without interference from the police. The penalty for holding an event without an entertainments licence is pounds 20,000 or six months in prison, but some organisers, who can make hundreds of thousands of pounds per rave, simply view that as one of their overheads.'
The Radio Investigation Service (RIS), part of the DTI's Radiocommunications Authority, is responsible for tackling radio piracy under Wireless Telegraphy Acts, amended by the 1990 Broadcasting Act. It has powers to seize radio equipment and prosecute the pirates.
Those found guilty could face up to six months in jail and, from October, fines of up to pounds 5,000. The penalties are often sufficient to deter the enthusiast who sets up a crude device in his front room. But the RIS is finding that they do not deter organised criminals.
All the components necessary to build a transmitter can be bought in most electronics stores for less than pounds 200. Once this is attached to an aerial, power supply, microphone and record and CD decks, the broadcasts can
The DTI investigators usually become involved when radio users complain about interference or, more disturbingly, when emergency communications are affected.
'Dance music has increasingly become an industry for hustlers,' said Lindsay Wesker, head of music at Kiss FM, the London-based dance music station that began life as a pirate operation in 1985 before winning a licence in 1990.
'They are getting into pirate radio because of the money they can make; not from advertising, but from organising club nights or unlicensed raves. It's quite simple - if they get a thousand people to pay pounds 20 a ticket for a rave, then they've made a lot of money. Then they sell Coke at pounds 2.50 a can and they have buddies who will go in and peddle their wares. People would not dream of going to a rave without taking something. Pills are a part of it - taking a tab of E (ecstasy) is as much a part of it as dancing or chatting up a girl. The whole buzz comes from dancing as long and hard as you can, but violence has come on to the scene because of the drugs.'
Edward Leigh, Under-Secretary of State for Technology, said the use of pirate radio was not 'harmless fun'.
'Interference from the crude transmitters . . . spoils reception for radio listeners and affects the emergency services' communications. The organisations behind the pirate stations and the businesses that advertise on them will be pursued. Any broadcasters inciting . . . criminal acts would be liable to prosecution by the police.'
Det Chief Insp Burrell said the use of pirate radio was the next step in a natural progression of organised promotion using all the electronic and communications equipment available.
'The monitoring of pirate radio broadcasts has actually become a good source of intelligence,' he said. 'There is so much money involved, that organised criminal elements inevitably get involved. And pirate radio communications are harder to stop than fly posters or mobile phones. We have seen illegal raves with up to 7,000 youngsters, many of whom think nothing of spending pounds 100 a night.
'Admission ranges from pounds 15 to pounds 30 - if you have 7,000 kids there, that's an instant, tax-free, pounds 105,000 to pounds 210,000; then there are the amphetamines that the ravers take to keep dancing all night at pounds 20 to pounds 30 a time; and because ecstasy, in particular, dehydrates you, there are cans of soft drinks at about pounds 2 a can - and each kid will buy four or five of those. The money to be made is quite startling,' he said.
The use of pirate broadcasting has become attractive to the pushers for three reasons: it is very inexpensive, it bypasses licensed stations, which would not advertise illegal raves, and it is anonymous.
Touchdown Radio, a pirate station operating in London since April, organises its own club nights in London, but at licensed and legal venues. One of its disc jockeys, DJ Space, said drugs inevitably crept on to the scene, but without the consent of the station. Over the mobile phone the station uses to pass on rave information to its listeners, he added: 'There are drugs in all walks of life, but we are just in this for the love of the music.'
When asked to confirm that Touchdown was a pirate station, he replied: 'Absolutely] We have been going since April without being raided, which is a long time for a station.
'We are rigged up in such a way that they might be able to find the aerial, but we will get away with the transmitter before they catch us. We'd be able to save most of our gear in a raid. They'd have the aerial but we'd be gone.'
He said a DJ at a club night organised by a pirate station might earn pounds 50 for a one-hour stint. The club and station might share takings but he argued that they would not be high. And he said the sale of drugs was nothing to do with the station.
'It is possible someone who wants to sell drugs could organise it as a package, but big illegal raves are hard to put together these days because the police are on top of them so quickly.'