The passengers and crew of a helicopter that ditched into the North Sea were being reunited with their families yesterday after they were rescued from the waters 125 miles off the coast.

The 18 people on board the Super Puma Bond helicopter escaped on to rubber liferafts and waited for help to arrive after the aircraft plunged into the sea on Wednesday night.

An investigation into the cause of the incident was launched yesterday and BP suspended using Bond's fleet of three Super Puma E225 helicopters.

Bernard Looney, managing director of BP North Sea, said everyone was anxious to know what had caused the incident but patience was required.

He said: "We are pleased with the fact that 18 people, who last night were in the middle of the North Sea in darkness, are back onshore safely with at worst minor injuries and they will be reunited with their families. To say I am pleased is an understatement."

The Air Accident Investigation Branch will conduct an inquiry into the incident. The helicopter has reportedly lost its tail boom but experts have suggested that it was probably as a result of the sea landing rather than the cause of it, or the incident might have been catastrophic.

Michael Coull, watch officer with Aberdeen Coastguard, said: "As far as we can ascertain this appears to have been a reasonably controlled ditching - there was no contact with the platform at all. From our point of view everything was carried out in a textbook way, if anything like this can be called textbook."

The Super Puma ditched around 550 yards from the BP Etap production platform. Crew on board the platform watched the drama unfold in the pitch black and low cloud. They saw flares fired and the glow of personal emergency beacons as the men took to the helicopter's two liferafts.

A major rescue operation was launched, involving an RAF Nimrod, RAF Sea King, civilian aircraft and boats.

The 18 people on the Super Puma helicopter escaped on to rubber liferafts and waited for help to arrive.

The first group of survivors arrived at Aberdeen Royal Infirmary shortly before midnight on Wednesday night. The three men were cheered by staff as they went in, and were discharged an hour later. Yesterday, as daylight broke, the remaining 15 were shipped into Aberdeen Harbour. Said to be "in good spirits", they walked the short distance to a waiting bus.

The workers, many of them carrying bags, looked relaxed, a number of them smiling and one of them giving the thumbs-up to onlookers.

Mr Looney praised the pilots who managed to land the helicopter on the sea and all those involved in the rescue.

"This is about the professionalism of many different groups not any one particular individual or particular team and I think it is a testament to the industry in the North Sea that we have been able to do what we did last night," he added.

He said the Jigsaw system and equipment - a safety system that involves specialised support vessels, helicopters and high tech personal equipment - had been a key part of the recovery and rescue operation.

Only two of the passengers were BP staff and Mr Looney said he had spoken to them but only to ensure they had all the support they required and he had not asked about the incident.

Transocean confirmed that 11 of the passengers were their staff or subcontractors who were on their way to the Marnock platform but he said none was available to comment.

A crewman on board the BP ETAP platform told how the three men winched to safety had been taken to the platform before being flown to hospital.

One had told him that he thought the ditching had just been a "hard landing" until water started flooding into the aircraft.

"They were just a little bit shaken. Once they realised what had happened they started to get worried but then their training kicked in," he said.

"I would say they were incredibly lucky."

Squadron Leader Barry Neilson, of RAF Kinloss, described the scene when the RAF Rescue helicopter arrived.

He said: "The aircraft that had ditched was sitting upright on the water, although the tail boom was missing, and the crew and passengers had managed to evacuate the aircraft very successfully and were in their dinghies.

"It was very foggy out there and the first aircraft to arrive on the scene, the BP aircraft, had some difficulty letting down to the surface but succeeded, and lifted three of the crew out of the dinghy."

Flight Lieutenant Kevin Ross, 30, the navigator of the Nimrod from RAF Kinloss which co-ordinated the airborne activity to prevent the helicopters crashing in "zero visibility" praised the skills of the Super Puma pilot. "He was very skilled to be able to get it down and keep it upright," he said. "The pilot of the helicopter which winched up the survivors also did an amazing job."