Conservative peer Lord Ballyedmond, who was killed in a helicopter crash with three others - all now named - recently raised safety concerns with the aircraft's manufacturers.

Two pilots killed in the crash in Norfolk have been named by sources as Carl Dickerson, chief pilot at Haughey Air Ltd, and Lee Hoyle, a co-pilot at the company - which was owned by the entrepreneur who was one of the richest men in Northern Ireland.

The fourth man who died was named locally as Declan Small, 42, a foreman who worked for Lord Ballyedmond. He came from Mayobridge, Co Down.

Lord Ballyedmond, known as Edward Haughey until he was made a life peer in 2004, was chairman of Norbrook, the largest privately owned pharmaceutical company in the world.

His AgustaWestland AW139 helicopter came down in thick fog in a field in Gillingham, near Beccles, at 7.30pm yesterday.

It has now emerged that Haughey Air Ltd had lodged a writ against AgustaWestland over concerns about a helicopter it supplied.

The case was lodged in September last year and is understood to have included concerns about in-flight mapping systems.

Meanwhile, profiles for Mr Dickerson and Mr Hoyle listed information about their careers on business networking website LinkedIn.

Mr Dickerson lists his current job on his LinkedIn profile as being at Haughey Air where he says he started in May 2010, and writes that he is "currently working for a private owner in a corporate environment".

He adds that he has been "successfully satisfying the requirements of many diverse and demanding business clients, VVIPs and heads of states".

He said he is "proficient at working in pressurised environments", and adds: "I believe that my flying experience, strong work ethic, and professional demeanor (sic) are well suited to most aviation requirements".

Mr Dickerson lists as his location as Lancashire.

Mr Hoyle also lists his job on LinkedIn, writing that he operates "a VIP AW 139 for a private owner", and lists Manchester as his location.

He says he started at the company in October 2012.

Under the experience section, he says he was an adventure training instructor in "HM Forces Army" from 1989 to 1997, working as an instructor in skiing, paragliding, climbing and mountaineering.

The men have not been formally identified.

A spokesman for AgustaWestland said the company could not comment on possible defects with Lord Ballyedmond's AW139 VIP helicopter but said it was investigating.

Speaking from the company's office in Italy, he said: "We cannot comment now because we need to make internal checks to establish exactly what the situation is.

"We cannot yet comment on this accident because there is an investigation pending and there could be many causes, be them technical or due to human error.

"Obviously we are very much regretful of what happened and will support the ongoing investigation in any possible way."

In February 2012 an inquest heard that in-flight technology systems on board AgustaWestland helicopters should be improved after a crash which killed a friend of the Prince of Wales.

The mapping databases display the height of terrain such as mountains and whether certain areas are available to fly through but the four-day inquest in Belfast highlighted flaws.

The aircraft flew into the side of a cloud-shrouded mountain in the Mourne range in Co Down in October 2010 as it carried a shooting party back to England.

Lord Ballyedmond owned Gillingham Hall, a stately home near the crash site, according to the Register of Lords' Interests.

Norfolk Police confirmed that the helicopter had taken off from Gillingham Hall shortly before the crash.

The crash site is an area of between 150 and 200 square metres, including ploughed fields, the force said.

Today, the wreckage lay beyond hay bales which were torn apart by the impact.

A nearby tree, which had stood taller than those around it, had fallen to the ground.

Work was under way today to remove the bodies along with any evidence from the scene.

All four people on board the helicopter were pronounced dead at the scene after it crashed in a field containing a wooded area, Norfolk Police said.

Emergency services were called by members of the public who heard a loud crash, though Inspector Louis Provart would not say whether there was an explosion and refused to speculate on the cause of the crash.

The Air Accidents Investigation Branch has been informed and a team will be sent to investigate the crash, a spokesman said.

Lord Ballyedmond served in the upper houses of Britain and Ireland, in the Seanad in Dublin.

Ulster Unionist peer Lord Reg Empey, who has known the Haughey family for 25 years, said: "Lord Ballyedmond was one of the most successful entrepreneurs in Northern Ireland and indeed these islands."

South Down SDLP MP Margaret Ritchie said he was unique.

"He got up and at it and he possessed those attributes required to make you a successful businessman but he also was a major employer and a lot of families had connections with him through that."

Stormont Enterprise Minister Arlene Foster said: "Without doubt, Lord Ballyedmond was one of Northern Ireland's most successful entrepreneurs, and he was known for his leadership, integrity and global vision."

Fellow peer and Conservative party co-chairman Lord Feldman said: "His career in business was a remarkable success story. He was a great friend to our party and a loyal and supportive colleague in Parliament."

Roland Bronk, owner of The Swan House inn and restaurant in Beccles, said it was "very foggy" in the area last night.

Met Office forecaster Helen Roberts confirmed that large parts of East Anglia had been hit by mist last night.

The scene is 45 miles (72km) from the spot where four crew members died when a US military helicopter crashed on a training mission in a nature reserve in Cley-next-the-Sea, Norfolk.

In January, a Pave Hawk from RAF Lakenheath was taking part in a low-flying training exercise when it came down.

Norfolk police later confirmed the identities of three of those who died in the crash.

A spokesman said: "The three deceased we can name are believed to be, subject to formal identification procedures, Edward Haughey, Lord Ballyedmond, from Northern Ireland, Declan Small from Northern Ireland and Carl Dickerson from the Lancashire area.

"The fourth man has also not been formally identified but next of kin are aware."

Silver commander Superintendent Dave Marshall said: "Police, fire officers and AAIB investigators have worked tirelessly throughout the day to enable the recovery of the deceased from the site and this happened late this afternoon. We are now satisfied that primacy for the investigation can sit with the AAIB."

He added that surrounding roads are due to be opened to the public.

Prime Minister David Cameron said: "Lord Ballyedmond was a towering figure in Northern Irish business life, and passionate about peace and good relations north and south, east and west.

"He was a larger than life figure who was a great supporter of the Conservative party and a good friend to me."