By Dominic Casciani
BBC News community affairs
Three nights a week, Mark slips into a secret location and begins his talk show on Baseline FM, a black-led pirate radio station broadcasting across London.
This week's hot topic is the Birmingham riots - a discussion being held on dozens of pirate radio stations across Britain.
He doesn't know how big an audience he has, but he says he has had calls during his time from all over the city.
"I get a wide range of people - a lot of professional people too," he says. "There used to be a police officer. I've had barristers and ambulance drivers. It's a forum for black people all over the city to get grumbles off their chest."
Pirate Radio, the cuddly 1960s world that launched a dozen cheesy DJs, is today a different place. What started with Radio Caroline in a North Sea trawler is now a big business in cities across Britain.
And while most people are oblivious to its existence, the role of two stations in Birmingham in broadcasting the allegations of rape that sparked rioting in the Lozells area of the city, has highlighted pirate radio's role in predominantly black communities.
Ofcom, the media watchdog, says there are some 150 pirate stations, half of them thought to be in London alone.
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Some broadcast across just a few streets. Others, like Baseline, have the capacity to cover cities.
Lynx, a Birmingham DJ who has moved from the pirate world to legal community radio, says that these stations are playing a crucial role.
"These stations don't just play music - they keep communities informed as to what's going on," says Lynx who now appears on Newstyle, a station with a community licence.
"Pirate radio is not just about this protest, it gives platforms to local talent, helps create local events and communicates what is going on. They're not doing anything different to legal stations."
Fire services hit
Some of the most popular stations over the past few years in Birmingham include Sting, and Hot, both linked to the airing of the rape allegations.
But Birmingham's most famous station, People's Community Radio Link (PCRL), met its demise in 2004 when, after some 20 years it folded under the weight of large fines imposed on its founders.
Some felt PCRL had played a key social role. Its final shows before being raided discussed gun crime in the wake of the fatal shootings of local teenagers Charlene Ellis and Leticia Shakespeare.
The authorities argued otherwise in court: PCRL's dodgy signal had rendered the West Midlands Fire Service's radio network unintelligible.
"If the authorities don't allow people to have legal stations, then a community cannot discuss issues that affect it or share the music they are into," says Lynx.
"And if people don't have the means to communicate openly, then it goes underground."
The authorities don't however accept these arguments - and say that pirate radio remains a public menace.
Theys say there is danger of interference with legal signals, be it fire services or, in another Birmingham case, air traffic control.
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But in addition, according to Ofcom, many stations are fronts for criminal enterprises. While the individual DJs may be ordinary folk looking for music careers, some station owners have less innocent intentions, argue the authorities.
"We know that station owners charge DJs for slots on their stations and some are turning over more than £5,000 in untaxed income a week. Many raids on pirate stations have uncovered links to drugs," says a spokesman for Ofcom.
"We've had pirate stations playing a particular song as code to local gangs, telling them drugs are available for collection."
Ofcom's 75 officers (10 alone in Birmingham) carried out 1,021 raids in 2004, leading to some 52 convictions. Raids generally get transmitters (mostly on tower blocks or stuck to mobile masts) - but not the studios which are usually miles away.
But the watchdog has a mountain to climb.
"Last year we were broadcasting from a basement and the police came in to the premises looking for drugs," says Mark of Baseline. "They weren't any to find - but they did find us. It all happened live on air with me at the mic. They took our equipment and I got a caution.
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"It's a game of cat and mouse. I was speaking to one of their guys who was very friendly. He showed me a list of all the local stations they were after, with their areas and frequencies.
"They know that when a station works out that they are out looking for transmitters and studios, the word goes around the DJs on all the stations and people work together to keep ahead."
Ofcom says it's immensely difficult if not impossible to win this battle on current resources.
"One of the challenges is that within hours [of a transmitter being found] the pirate stations can be on air again," says the spokesman.
Given that entry costs have got cheaper over the years, a raid is seen by some pirate radio stations as an inevitable business expense, say insiders.
Even if everything was seized, transmitter, studio and associated kit, a basic broadcast could be back up within a day with less than £1,500 of equipment. This leads many DJs to believe Ofcom is turning a blind eye to stations that are responsibly run by avoiding conflicts with other signals.
Ofcom denies this, saying that it is a matter of priorities rather than preference.
For their part, West Midlands Police say that in general their officers pass on relevant intelligence to Ofcom as the agency repsonsible for tackling transmissions.
On the weekend's events, a spokesman would not be drawn on whether the force would be investigating stations for incitement to racial hatred, or other offences.
While Ofcom largely prioritises raids on stations whose signals interfere with the emergency services, this does nothing to prevent the broadcasting of what could be incendiary views - the key issue being debated in Birmingham.
Ofcom can use its powers to deal with legal broadcasters who break its code.
But many pirate stations build an audience on strident views. One south London station is notorious for its presenters' uncharitable views of white people; rather ironically, its signal very often cuts across that fortress of Middle England, BBC Radio Four.