Air accident investigators are calling for better training for helicopter pilots after a crash which almost killed TV gardener Alan Titchmarsh.

The accident could have been caused by freak storms, an air accident report has revealed.

But investigators are now calling for better training for pilots flying the type of helicopter used by the Titchmarsh and his BBC camera crew when it crashed just yards from Hadrian's Wall last May.

The 1967-built Bell Jet Ranger was destroyed at Sycamore Gap, a beauty spot made famous in the film Robin Hood, Prince of Thieves. It landed yards from where the former Ground Force presenter was standing.

But he, the pilot and two members of a camera crew on board, managed to jump clear as it came down.

A report from the Department for Transport's Air Accident Investigation Branch, said the 39-year-old pilot lost control of the aircraft.

Investigators found no evidence of any mechanical failure but said freak wind gusts caused by thunderstorms in the region and a safety issue with the tail rotor in the type of helicopter involved could have contributed.

Witnesses described a plume of smoke rising from the helicopter and said it appeared to be struggling before it fell. Farmer Willie Weatherson, of Edges Green Farm, Haltwhistle, who was first at the scene, said yesterday: "We could hear the helicopter from half-a-mile away and there was no question in my mind there was some sort of mechanical problem.

On the day of the accident, Titchmarsh was filming a new series called Britain Through Time.

After a practice run, the helicopter swayed to the right as filming began.

The pilot tried to correct the turn, but realised it was out of control and decided to crash land.

Investigators are now calling for better training for pilots using the Bell Jet Ranger series after a safety examination carried out in America in 1995 found they were susceptible to "unexpected right yaw," (sway) particularly at low altitude, low speed flights.

Bell Helicopters issued safety recommendations in the 1980s on how to correct the problem if it occurred.

The accident report said that it appeared possible that the pilot had experienced loss of tail rotor effectiveness (LTE).

"The phenomenon is not widely known in the UK. It is therefore recommended the European Aviation Safety Agency should be approached with a view to having information on LTE included in helicopter pilot training," it added.