Anti-war protesters hijacked national radio to promote a peace rally in Brighton on Friday night.

Listeners to the 1pm BBC Radio 4 news bulletin yesterday were stunned to hear a pirate broadcast, promoting the demonstration in Brighton, cut in over the scheduled programme.

The BBC antenna at Whitehawk Hill was not tampered with and investigators suspect the broadcast was made from another transmitter in the city working on the same frequency.

They are now keeping a careful watch on the station's output to check any unlicensed transmissions.

Brighton resident Brian Oram said: "I just turned on the radio for the 1pm Radio 4 News on 94.5 FM.

"There was a normal start to the programme for about 60 seconds then a big hiss and another broadcast started.

"A non-BBC male voice started going on about Kate Adie and unauthorised satellite uplinks being targeted by US forces.

"It went on for about one minute, then changed to an anti-war speech requesting large support for an anti-war demonstration in Brighton."

Another listener, Tony Howard, said he had radios tuned into different Radio 4 transmitters and said only the Brighton antenna was affected.

He said: "This strange voice came on and started talking about the Gulf and it mentioned Community Base."

Community Base, on Queen's Road, Brighton, is a centre for a number of charitable groups and local organisations.

Director Colin Chalmers said: "We received three calls from people who heard the broadcast. The first said they heard us mentioned and the second thought it was actually being broadcast from Community Base, which was worrying."

Crown Castle, which operates BBC transmitters, was unable to comment as the matter was under investigation.

A spokeswoman for the Radiocommunications Agency said: "I can confirm an illegal broadcast interrupted the licensed radio channel."