Truth is stranger than fiction, as this incredible documentary attests. Had its events been written in a novel you would have dismissed it as totally outlandish, and yet everything in The Sex Change Spitfire Ace (Channel 4) is completely true.

As with a far-fetched, overwritten novel, the events are set in the 1940s and 50s, a time of war, tragedy and noirish glamour and - that novel again – its events encompass dreamy Oxford, a wartime hero, a dashing daredevil at the racetrack, steamships, baronets, corpses, broken families, unrequited love and suspected suicide.

Michael Dillon was convinced he was in the wrong gender. Born as Laura, he began to bind his teenage breasts but was told by school friends this would give him cancer. Frustrated in attempts to conceal his blossoming female body, he was aggravated and miserable until going up to Oxford. There he found the confidence to cut his hair and begin dressing as a man, but these were mere cosmetic changes.

Meanwhile, Bob Cowell was pursuing his passion as a racing driver, the speeding cars being “a symbol of power, courage and virility.” Also, he’d served in the Second World War as a Spitfire pilot. Can we imagine any pursuits more macho than those? Yet he secretly felt he was female: “this isn’t really me.”

As Cowell indulged in brash demonstrations of masculinity, trying to keep at bay any thoughts of femininity, Dillon was going the opposite way, and taking testosterone. The drugs soon meant he was shaving and acquiring some bulk, yet he remained desperate for a sex change operation even though such a thing was incredibly risky in the 1940s.  

He sought help from Sir Harold Gillies, then the top plastic surgeon in the country, a man who’d developed his expertise in treating war casualties, including men who’d lost their genitals in combat. This latter group were treated by rolling up flaps of skin into “a tube which can be a very effective penis”.

There followed some very graphic images of flesh being rolled, pinned and stitched into a replacement penis. Although rather disturbing to anyone who flinches at medical procedures, this was important, not freak-show titillation, as it may help dislodge some of the disgust people feel towards the transgender community by showing that their “transition” belongs to medical science, just as an appendectomy or broken arm does. It is a situation which requires surgical help, not a grotesque mystery.

Of course, some insight into the surgical side cannot begin to shed light on the huge hinterland which lies behind it, but it might be a small start. We can’t know what brings a transgender man or woman to the operating table – that’s a task far beyond a 60 minute documentary – but it reminds us he is a human being, not a freak or an oddity; just a person who needs some treatment from a doctor, as we all do.

As Dillon was confronting the surgery which would give him the man’s body he needed, Cowell was seeing a “medical sexologist” who validated his feeling that he was a woman, giving him the push he needed to leave his family and begin life as a female. He took pills to soften his features and give him breasts, and changed his name to Roberta.

Yet Roberta had a greater difficulty than Michael. Michael was able to have surgery to build him a penis, but a vice-versa operation would be illegal: no doctor practicing in Britain was allowed to remove a penis without a medical reason, and a “sex change” wouldn’t count.

By this point, Roberta and Dillon had met and discussed their various problems, with Michael Dillon falling madly in love with Roberta, writing her passionate love letters where he said he needed “two whiskies in me” before being able to speak of love. But Roberta wasn’t interested in Dillon’s love; he simply wanted his “medical connections”. Dillon had been through sex change surgery and Roberta wanted the same - even though his requirements were illegal.

A British doctor would be able to reconstruct and create new genitals for Roberta, but he wouldn’t be able to remove the penis – the essential first step in the process - so Dillon, blinded by love for Roberta, gallantly agreed to do it for him. He volunteered to castrate Roberta, and she could then legally present herself at a surgeon’s and ask for a vagina to be built in its place. (Of course, Dillon didn’t want to botch the job, so he practiced on a corpse first.)  

The entwined story of this man and woman was simply incredible. Both achieved what they wanted - a transition into another gender - at a time when society and science was frowning upon them, and yet both stories ended sadly, with Roberta shunning her children and forbidding them from entering her new life, and Michael never able to find peace or acceptance, even when he fled to the Himalayas to become a monk.

Even getting what they most desired didn’t achieve happiness, and that’s another reason why this story could never be a novel: it’s just too sad and grim. Real life keeps intruding on this most spectacular of stories, ensuring there is no happy ending even when they get their heart’s desire. There always remains the litter of abandoned children, alienated families, rules, routines and prejudice.