The Portland Coastguard crew had to evacuate the helicopter after making an emergency landing at the Royal Marine barracks in Poole on Monday afternoon.

Flames consumed so much of the helicopter's engine that the aircraft will have to be scrapped, said a spokesman for the Marine and Coastguard Agency.

The rescue crew were out searching for a man believed to have fallen out of his dinghy in Poole Harbour, Dorset when the pilot reported engine difficulties.

The Sikorsky S61N Mark Two

Seats up to 19 Maximum speed 131 knots (150mph) Has auto hover and infra red camera to search at night Airborne within three minutes of emergency call

The helicopter was a quarter of a mile out to sea when it had to turn back to make an emergency landing.

A Dorset police helicopter was scrambled to continue the search for the missing man.

The Air Accident Investigation Branch has been informed but other Sikorsky S61N helicopters based at Lee-on-the Solent, Stornoway and Sumburgh will not be grounded, the spokesman said.

A spokesman for Bristow helicopters, which leases the specially-equipped helicopters, said: "This has never happened before.

"It has an excellent safety record. It's a hugely reliable aircraft which is why they are used for search and rescue operations and they are regularly overhauled and maintained."