Mixed-race people once faced discrimination and hostility in Britain, so how much have things changed?
It's only when Frances and I go back and look at our wedding album that we realise quite what a meeting of cultures our marriage was. Not so much for the two of us but for our parents. My mum in her red and gold sari and Mary, my mother-in-law, in her floral patterned suit - it sort of sums up the journey the two families were making.
The truth is that Frances and I were wilfully ambivalent about the challenges that our different heritage and colour might throw our way. But not everyone around us was quite so sanguine. Years after we got married in 1984 we heard about a conversation between Frances's father, Charles, and her grandfather.
"Is this Ala-what's-it educated?," the older man had asked.
"My dear man, that boy is more educated than you and I will ever be," was Charles's reply. It was quite a retort coming from a man who had himself studied at Oxford.
But even Frances's father, who had stuck up for me so eloquently in public, had felt the need to have a private word with her once we had announced our decision to marry. In his gentle way this country solicitor told Frances that life for us - and our children - might be just that bit more sticky than it might otherwise be. That was then, this is now.
In London - indeed in any of the UK's great cities - mixed-race relationships are so common that it would be strange to notice them at all.
Mixed-race children make up one of the fastest growing ethnic minorities in the UK. According to some census experts the number of mixed-race people in Britain will double between 2001 and 2020, when demographers predict it will reach 1.3 million people.
Far from being saddled with disadvantage - my father-in-law's instinctive fear - the latest evidence suggests that most of these children are born into more stable, middle-class families than the popular stereotype would suggest.
Mixed-race people are among our most famous and high-achieving citizens - there's Zadie Smith, Chuka Umunna, Lewis Hamilton and Leona Lewis to name a few.
Yet it's not so long ago that to be born mixed-race in Britain was to carry a burden of shame and opprobrium. While filming Mixed Britannia for BBC Two I interviewed Connie Ho. She was born in 1921 to a Chinese father and a white, English woman.
I met Connie in Limehouse, the original Chinatown, with her great-grandchildren. She remembers vividly how she and other mixed-race children were taken to an upstairs room above a restaurant to be measured by scientists.
They recorded the distance between her eyes, the width of her forehead, the colour of her eyes and carried out a host of other pseudo-scientific tests. This was in the 1930s, the heyday of the eugenicists and their fascination with mixed race children was far from benevolent.
It wasn't until the Holocaust laid bare the revolting use that eugenics had been put to in Hitler's Germany that British champions of the flawed science recoiled in horror.
The truth is that for most of their history in this country, mixed-race people have been, at best, tolerated and, more commonly, treated with revulsion and abuse.
Like most people I had always assumed that mixed-race communities, with their own defined space and culture, really only began with the mass immigration of the late 1940s and 50s. How wrong I was.
On a freezing cold morning in March, I knocked on the door of a rather dilapidated mid-terrace building in South Shields. Inside, Abdo Obeiya and Yahia told me about the Yemeni cafes and shops that had once lined the streets near the harbour.
Like veterans from a forgotten war they told me how they used to sweat their way through months-long voyages in the underbelly of a steamship, feeding coal to the ever-hungry furnaces. They were, literally, stoking the fires of commerce.
They were not the first of their kind. Their fathers had done it before them. That would have been in the early 1900s.
Trade and empire - the foundations of British wealth - are the reasons why these men from a desert nation ended up braving the chill winds of winter in far-away Britain. In Cardiff, Hull, Liverpool, Bristol and London the story was the same.
Young men, spruced-up in their shore suits, stepped off the gangway and found fun, companionship and love in the arms of British women - together they changed British society forever.
It was love in a cold climate. The women who took up with these seamen were more often than not cut off from their families. They were accused of being "sluts" and their children described as lice-ridden half-breeds.
Surrounded by this wall of prejudice and rejection they still managed to build communities of genuine warmth and cohesiveness, truly multicultural before the term had ever been conceived.
In Tiger Bay, Eid ul Fitr, the festival that marks the end of the Ramadan fast, was celebrated by Muslims and Christians alike.
These early mixed race communities made it up as they went along, unhindered by the rigid political correctness and religious righteousness that would come along later.
Norman and Maureen Kaier - both of them the products of Yemeni/English unions - told me how their mothers kept a separate pan for frying bacon.
No sooner had their Muslim fathers stepped out the front door than the delicious aroma of an English breakfast wafted through the terraces. Everyone knew what was going on and nobody made a big deal of it.
The determination of these women to fall in love with the man of their choice was an act of feminism, even though most of them would never have thought of describing it as such. What they lacked in conventional education and status they more than made up for with sheer guts and heart, no more evident than when they defended their men in the race riots of 1919 and later.
Women like Emily Ah Foo were heroic pioneers. Under some arcane interpretation of legislation designed to intern Germans in Britain during the Great War, Emily, a full-blooded English woman, was forced to renounce her birthright when she married a Chinese seaman, Stanley Ah Foo.
She was deemed an alien in her own land. The injustice and humiliation still rankles with her mixed-race daughters Lynne and Doreen, now in their 80s.
The road to social acceptance has been a long and rocky one. In the 1940s, the children born to white women and black GIs stationed in Britain were described as "war casualties" here and, in America, one congressman called them the "the offspring of the scum of the British Isles".
These affairs, forged in the uncertainty of nations at war, produced a thousand or so babies. As it happens, my brother-in-law Tony Martin, was one of them.
Like so many of the "brown babies", as they were called, his mother handed him over to Barnado's, unable or unwilling to face the public distaste she would have had to endure if she tried to raise him herself.
Tony was one of the lucky ones. He was fostered by a family, the Tabors, in the village of Balsham, near Cambridge and whenever we've talked about his early life he's always remembered it as a period of undiluted joy.
I knew he'd met his natural mother but it wasn't till I interviewed him for Mixed Britannia that I discovered there was an occasion when she had asked him to live with her. But he was happy where he was.
One can only imagine the heartache of this young woman.
What I've realised shooting Mixed Britannia is that it's not really a history of race but about Britishness - that elusive quality we all understand instinctively but find so difficult to encapsulate in words.
The UK was subject to the same prejudices and pressures as the US and Germany yet we avoided the worst excesses of bogus science or political extremism. There were calls for anti-miscegenation laws - but we never banned mixed marriages.
True there were ghettos - but the UK never accepted outright segregation. There were - and are - plenty of racists, but they've never been allowed to gain the foothold they did elsewhere.
Somehow - often by default rather than design - we have muddled through to where we are today, a country largely at ease with its rainbow people. Given what's happening elsewhere that is something to be proud of.