Forget Winston Churchill, this is the man who really helped win the Battle of Britain

The stirring words of Spitfire designer Reginald Mitchell have entered legend. "I'm going to build a plane that will move just like a bird... I want to build a fighter. The fastest and deadliest fighting aeroplane in the world." There's just one problem, the chief engineer at the small firm of Supermarine never uttered them. They come from a clifftop scene in the wartime propaganda film, The First of the Few, leading generations to believe Mitchell designed the Spitfire pretty much single-handedly while persevering against painful cancer.

While there's no disputing Mitchell was a national hero, he didn't create the Spitfire alone. It's true he had rectal cancer but much of the 1942 film, starring and directed by Leslie Howard as Mitchell and featuring David Niven, is fabrication.

So let's explore the real man: a true national treasure. Over the years I've become increasingly frustrated with the liberties taken with facts about the Spitfire and its creation. As we mark the 85th anniversary of the Battle of Britain this year, it was time, I thought, to find the real Reginald Mitchell. And the truth is, he's much more brilliant than we ever suspected.

Mitchell was the father of the Spitfire. But he was not the sole designer of the aircraft; he created a team of some of the most talented young men - and a few young women - available at the time. He offered jobs to those with skills across the industrial sectors. They learned on the job and were rewarded well. Most "Supermariners", as they were known, were lifers.

The Supermarine S6b racing seaplane, winner of the sought-after Schneider Trophy in 1931, was the fastest flying machine of its day and the first to break the 400mph barrier. It proved a string of new technologies. Mitchell and his team in Southampton took the most advanced materials of the time, including Duralumin aluminium cladding, and engine cooling know-how from the Schneider Trophy-winning aeroplane and started to design a fighter plane. At first they failed but they persevered.

New technologies included the prototype Rolls-Royce Merlin engine, which powered a generation of fighters and bombers - not just the Spitfire and Hurricane during the Battle of Britain but the Mosquito and Lancaster too. The Merlin was the direct result of the aeroplane maker and the engine design team working together.

Both Mitchell and Sir Henry Royce had been trained in the railway industry. It showed that they understood teamwork. At the turn of the 20th century, railways were the technology leaders. They were trendsetters in Britain's industrial heartland. Everyone wanted to sign up to be trained as apprentices. University engineers were few and far between.

Growing up in Stoke-on-Trent, Mitchell was keen as mustard on flying machines - a builder of model aeroplanes who wanted to become an engineer. But aviation jobs were scarce and apprenticeships were simply not available. He was the son of a master printer from Yorkshire and a devoted mother from the Potteries. He had a loving family environment where he was allowed to develop his engineering skills in parallel to his school work. His father converted a coach house for him, supplied the right tools and helped him learn.

Mitchell subsequently started his career as an apprentice at Kerr, Stuart & Company, the foremost specialist locomotive builders. That brilliant grounding led this man to become renowned for engineering excellence. Yet, somehow, railways weren't big enough for Mitchell - or RJ as most knew him. He wanted to build aeroplanes and play his part in the war effort. He was exempt from First World War military service but had to do something constructive, so he applied to be the assistant to the boss of Supermarine in the Southampton suburb of Woolston.

In 1916, Southampton was the gateway to the Empire. The docks were busy loading supplies for the Western Front. Troops were marching aboard ships to take them to France. The whole place was alive when Mitchell stepped off the train from London. His job interview led to an immediate appointment at Supermarine working on Admiralty flying-boat contracts. The die was cast. He would spend the most productive 20 years of his life at Supermarine and create world-beating designs.

He initially took war-surplus flying boats and converted them. He worked on innovating the design, hull form and flying characteristics. This became the basis for his Supermarine designs - 24 different flying machines in 20 years.

His boss, Hubert Scott-Paine, was a speedboat enthusiast keen on self-promotion, so the team entered the Schneider Trophy competitions of the early 1920s. The trophy was the most prestigious event of its time, drawing up to a million spectators to its racing seaplane heats in Monaco, Venice, Chesapeake Bay and eventually Cowes. It became the World Cup of the age. Early successes were great marketing for the firm but didn't pay the bills.

So Mitchell set to work on creating a world-beating, long-range aircraft to open up the Empire to British air policing. The Southampton flying boat was way ahead of its time both in military capability and crew comfort. But the greatest challenge of all was winning the Schneider Trophy for Britain permanently. That required three straight wins, which was a tall order without government assistance. Rival nations France, Italy and America all had various forms of official sponsorship for their Schneider entries.

Britain, initially, had none. Mitchell worked on the winning designs: the S5 in 1927, S6/S6a in 1929 and then the S6b in 1931. That last win nearly didn't happen. It needed the intervention of an angel funder called Lucy Houston. Lady Houston was a political powerhouse who shocked the Ramsay MacDonald National Government into supporting Mitchell and Supermarine. The Royal Air Force reformed the High Speed Flight, a specialist unit of its best pilots and, just in the nick of time, everything was ready.

Britain had the best flying machine with the best engine flown by the best pilots and the best chance. The venue for this vital race was RAF Calshot and the race track was the Solent. Everything was set. A million people travelled by special train to watch 1931's greatest sporting event. On the afternoon of September 13, Flight Lieutenant Boothman took the S6b to a record top speed of 340mph over seven laps of the Solent.

Britain, Supermarine and Reg Mitchell had won the Schneider Trophy for Britain. Then, two weeks later, Flight Lieutenant Stainforth broke the 400mph barrier in another S6b. Almost the same day, the Air Ministry issued a specification for a new all-metal fighter aeroplane with clear intentions to use the advances made by Reg's team.

Supermarine's first attempt, the Type 224, was a failure but Mitchell and Supermarine persevered. With his trusted inner circle, including Alf Faddy, the design team leader, Beverley Shenstone, the wing aero-dynamicist, and Alan Clifton, his assistant, Mitchell went back to the drawing board and created the Type 300. It was ready for a first flight on March 5, 1936. It looked like a winner.

Today, we call this design the Spitfire - probably the world's most iconic aeroplane. But Mitchell was now gravely ill with cancer. Knowing he could leave the Type 300 in the hands of his trusted lieutenants, he wanted to create the world's best bomber.

The B12/36 - it never had a name - would fly higher, faster, further, with more bombs and greater crew comfort than any previous aeroplane. Mitchell worked with Shenstone on a load-carrying elliptical wing in a structure that would be pressurised for operations above the reach of "flak" and most enemy fighters. It would be fast - 100mph faster than its rivals from Avro (Lancaster), Handley Page (Halifax) and Short Brothers (Stirling). The latest engines from Bristol or Rolls-Royce would make it a world beater.

Sadly, it was not to be. When Mitchell died in 1937 aged just 42 and never having seen his Spitfire in action, the B12/36 was still only a wooden mock-up. It would be destroyed in September 1940 by Luftwaffe bombing. With tensions rising across Europe, Supermarine, a cottage industry at best, had to use everything in its grasp to get the Spitfire into production and machines to RAF Fighter Command. So the Bomber project was abandoned.

The first Spitfire was not delivered until August 1938 but, when it arrived at RAF Duxford, it was a clear winner with pilots and groundcrew alike. How sad Mitchell never lived to see the Spitfire enter service. He missed the sterling performance in every theatre of war, and he never was able to apply his engineering skills to the jet engine. Imagine a Mitchell jet fighter!

• Mitchell: Father of the Spitfire, by Paul Beaver (Elliott & Thompson, £20) is out now