The distress signal was tracked by Ofcom investigators in Belfast among a mountain of old fridges and television sets in a scrap metal yard at Queen's Island.

The beacon had been activated after it was dismantled from the vessel and dumped in a scrapyard in north Belfast. The beacon's emergency radio signal was picked up by satellite and by the Civil Aviation Authority's receivers on the Isle of Man last Thursday.

The emergency beacon is designed to transmit a ship or aircraft's identification when it is in need of help.

The satellite can identify the ship's location and a rescue helicopter is normally scrambled.

However, in this case RAF Kinloss was able to tell that the ship apparently in distress was actually on land somewhere in Belfast.

Ofcom investigators were called in to trace the beacon and their search led them to a scrapmetal yard on Queen's Island in Belfast's docks.

Ofcom is responsible for monitoring all radio broadcasts and for investigating cases of interference.

Philip Morgan, spectrum manager for Ofcom Northern Ireland, said the signal had to be switched off because it was interfering with radio systems.

He said: "Once we had established that the beacon wasn't coming from a ship in distress, we had to find it and switch it off because it was causing interference to the CAA's radio system - and these beacons can go on transmitting for a considerable time once they are activated.

"The satellite tracked the beacon as it was moved by a scrap lorry from a site in north Belfast down to the Queen's Island site in the docks.

"There we were able to trace it to the middle of a pile of old electrical equipment 20ft high.

"It was a bit like looking for a needle in a haystack, but using our radio tracking equipment, and with the help of the scrapyard's crane, we were able to find the beacon very quickly and disable it within a couple of hours of it going off."

Ofcom Northern Ireland investigates up to half-a-dozen cases every year of distress beacons from ships or planes being activated accidentally.

Philip added: "We would remind boat and plane owners that these emergency beacons are designed to be sensitive and they should be handled carefully and disposed of responsibly.

"Otherwise they can cause a false alarm which wastes the rescue services' time and could divert them from a genuine emergency."