It all began with makeshift transmitters in baby prams and a group of teenagers running from the law.

But now Tolworth-based Radio Jackie is celebrating 40 years since its first pirate broadcast on March 19, 1969, and will mark the occasion with a party this Thursday.

It is not a true 40th birthday for the south-west London radio station, which shut down for 18 years after it was raided for not having a licence in 1985.

The station is now on the right side of the law, and was relaunched in October 2003 by the original management team which reformed to purchase the loss-making station Thames 107.8.

Mike Knight, 57, who was the first voice to grace the airwaves in 1969 and to this day has a Sunday show, spent 28 days in Pentonville prison in the 1970s for illegal broadcasting on Radio Jackie.

He said: “It was always clear that fines were not going to stop me. They suspended a prison sentence and that didn’t stop me so the chairman of the bench in the magistrates’ court suggested a short, sharp shock in prison and that had no effect either.”

He and his teenage friends were so desperate to get on air that they set up mobile home-made transmitters and pushed them round parks, wrapped up in blankets in a pram. One of their mothers even came on board to take phone calls at her home in Sutton.

Constantly on the run from the radio regulators, they originally broadcast for 30-minute slots on a Sunday as part of a network with other pirate stations, but this was deemed a disaster because of patchy reception.

The station expanded to become 24-hours-a-day in the 1970s, putting out party political broadcasts, taking advertising and paying staff and taxes, all while still technically illegal. Former staff include Radio One’s Dave Pearce and TV hypnotist Paul McKenna.

A widespread campaign to get a licence in 1984 failed, despite getting a 55,000 signature petition and support from the council, and the station was raided for a final time in February 1985.

Mr Knight still believes the essence of the station has remained. Despite it no longer being pirate, it plays a similar mix of mainstream “non-extreme” music, he said.

Station owner Tony Collis added: “I remain absolutely proud of our fight against the establishment. I think what we did, as pirates, changed the face of radio forever.”