In the summer of 1940, Britain defied Hitler's Nazi Germany in a crucial battle that became a critical turning point in the entire war. Over the intervening years it has become a well-told story of Spitfires and Hurricanes tussling against the over-mighty Luftwaffe in the sun-drenched skies of southern England. But the reality was far more complex – and even more exciting and dramatic. So while 70 years on, it is absolutely right that we should still commemorate those incredible days, it is also time to look beyond the myth. And that is what we have done in Battle of Britain - The Real Story, which is broadcast on BBC2 tonight.

Researching the Battle of Britain from a UK perspective is a straightforward affair: there are a plethora of books on the subject (Britain has some of the best archives in the world) and a number of veterans willing to talk about their experiences.

Trying to piece together what happened that summer from the German perspective is a different kettle of fish. If the survivors who flew for Fighter Command back in 1940 are the few, then those who fought for the Luftwaffe are the even fewer. Unlike the RAF, the Luftwaffe did not really rotate their pilots: most simply flew and flew and flew.

In addition, a large number of those who did somehow survived were then captured by the Russians and had to endure lengthy stints in gulags, which did little for their chances of longevity. When I began researching the battle there were about 25-30 Luftwaffe Battle of Britain veterans left; now you can count them on just two hands. Even if you can track them down, most are not that eager to be interviewed by a British historian about a battle they lost in a war they have since been vilified for. I was lucky to find someone who knew many of them and was able to set up the interviews for me.

At the National Archives in Kew, anyone can look at the squadron diaries, or operational record books, as they were called, with great ease, but a large number of the Luftwaffe records were destroyed at the end of the war and the German equivalents are often only fragmentary and sometimes do not exist at all. But records, diaries, personal papers and post-war interrogations and interviews with senior commanders – mostly carried out by the Americans – do exist, and by painstakingly scouring through as many archives as possible, piecing together the German side of the Battle of Britain was and is possible.

One of the most extraordinary personal accounts I came across was in a tiny archive in Emmendingen in the Black Forest. There I found the diary of Siegfried Bethke, a German fighter pilot who had joined up in 1935 at the Luftwaffe's birth and was still flying at the war's end. His day-to-day record of the summer of 1940 was full of insights that I had never really considered before.

The problem with our tendency to look at the Battle of Britain from a purely British perspective is that it has led to an inaccurate picture of Germany's strength and how it viewed the battle. We have almost completely written out the contribution made by Bomber Command, for example, yet the Germans were seriously troubled by these raids. And while 1940 was unquestionably Britain's finest hour, study of the German battle shows it to be a story more compelling and dramatic than the myth we all know.

Battle of Britain: The Real Story is broadcast tonight at 8pm on BBC2