After a career working for Airbus and BAE Systems – ending up as the leader of the programme to build the "A400M" military aircraft by the time of his retirement – you would forgive David Bradley for never wanting to see another half-built aeroplane again in his life.

Back in 2003 when he left the company behind, he had mapped out all that he would do with his retirement – it was the perfect opportunity to indulge himself by building that model railway he had always dreamed about and renovating the dilapidated 1967 Lotus Elan that had been rusting in his garage for decades.

But then an intriguing new opportunity came up, and David simply couldn't say no.

"I joined up as a volunteer with the Bristol Aero Collection – which is currently stored at Kemble Airfield, but which we eventually hope to house in a special museum with Concorde at Filton.

"Soon after I joined the organisation, I heard about this Bolingbroke bomber that they had bought from a collector in the United States. I knew the plane needed a lot of work to get it looking fit for the museum, and it seemed like a great challenge.

"Before I knew what was happening I had volunteered to lead the project, and the model railway and renovated Lotus had to go back to being pipe dreams."

Almost three years on, and the Almondsbury pensioner is driving me across the airfield at Filton, to an unremarkable-looking aircraft hangar opposite Concorde –the airfield's permanent supersonic attraction.

"Airbus has been good enough to lend us this hangar to work in," David explains. "It's very handy, because previously we had bits of the Bolingbroke being worked on at different people's houses all over the place. The hangar is an original World War I facility – dating back to 1917, so it's quite an atmospheric place to work."

David opens the great metal doors, which reveal the silhouette of a rear fuselage. As the fluorescent lights dance into life above our heads, the shape becomes clear as the Bolingbroke bomber, or at least, what remains of it.

Though it looks in a sorry state at the moment, this aircraft once served to defend the skies above Alaska, after the American air force was all but obliterated at Pearl Harbour. This is one of the lucky few of the cramped bombers to survive the war.

"The aeroplane spent more than 60 years outside, left to rot in a farmer's field in Canada," David says. "So when we got her, she was a shadow of her former self, but we're determined to get her back into shape. There simply aren't many of them around. The Bolingbroke is the name given to the Bristol Blenheims that were built in Canada to Filton's exacting drawings for the Canadian air force.

"To all intents and purposes it is a Blenheim, which is one of the most significant aeroplanes ever to come out of Filton."

The Blenheim was launched in 1936, with Lord Rothermere, owner of the Daily Mail, a keen advocate for the aircraft – he was desperate to point out that the 300mph passenger and cargo plane was, at that time, quicker than any of the Royal Air Force's fighter aircraft.

"He was trying to get the Government to buck its ideas up, and was keen to show that a private company was capable of making better aircraft than the Ministry of Defence," David says.

"After seeing the aeroplane's capabilities, the Government was quick to order a bomber version of the plane for the RAF. When war broke out, the Blenheim became the first Allied plane to be used in the conflict – it was used to carry out the first sortie of the war on September 4, 1939, just 24 hours after the declaration.

"But by the end of the war, her technology had been overtaken by many much faster fighter planes, which meant that Blenheims and Bolingbrokes were butchered in the skies over Germany.

"After the war the RAF melted down every single Blenheim that was still in existence, but the Canadian air force sold their remaining Bolingbrokes as 'unusable aircraft'."

The actual plane that is standing before us in the Filton hangar was bought by a farmer in Manitoba, who removed parts such as fuel tanks and hydraulic jacks, before abandoning it in a field until 1972.

It was then bought by an aircraft enthusiast from California, who had intended to renovate it. But the intimidating task proved a little too ominous, so it remained outside his home until the rusting hulk was finally bought by the Bristol Aero Collection in 2006.

"We had it hauled by truck right across America, and then shipped into Liverpool," David recalls. "That was a 6,000-mile journey, but we were able to do it thanks to a tremendous amount of logistical support from BAE."

David's team of a dozen or so volunteers have been lucky to have the support of a number of businesses and organisations, as well as BAE Systems/Airbus.

"Messier Services at Cheltenham took on the restoration of all the landing gear as a formal apprentice training programme," David explains, "and the City of Bristol College took the centre wing section for restoration at their aircraft engineering training centre. The Rolls-Royce Heritage Trust agreed to take on the restoration of the engines and their ancillary equipment in their workshop at Patchway."

It's a short drive from the airfield to the Rolls-Royce Heritage Trust workshop where we find volunteers Jim Hook, 72, and Patrick Loney, 82, at work on the engine restoration.

For Jim, who retired from a career at Rolls-Royce nine years ago, and widower Patrick, a former engineer at the Berkeley power station, the two days a week of volunteering on the project allows them to keep their hand in at the sort of workshop where they spent much of their working lives.

"We love it," Patrick says. "For us, this is our great interest. It certainly beats sitting at home."

David believes it could take as much as three more years of work before the aircraft finally comes together, by which time he hopes there might be a new museum for it to be displayed in at Filton Airfield.

He says: "It will be brilliant when we finally see all the pieces come back together. This is an important part of Filton's history that we're preserving – that's why it's so terribly important."