Last weekend, I had The Conversation for the 3,897th time – and this time, it took place in central London just two roads away from the hospital where I was born. As usual, it went like this:

Stranger: Where are you from? [Translation: You look a bit brown. Why are you brown?]

Me: London.

Stranger: No, where are you really from? [Translation: You are clearly telling me untruths. Brown people do not come from London.]

Me: London.

Stranger (exasperated): No, where are your parents from? [Translation: Now you're just being obtuse.]

Me: Africa and America.

Stranger (confused): Erm … so where are your family from, like, back in the day? [Translation: People who come from Africa and America do not look like you.]

Me: Iran, India, Africa, America and England.

Stranger (relieved): India and Iran! Do you ever go back?

At this point, I have to explain that it's hard to go back to somewhere you have never been. I've lived in London since I was a zygote, have a London accent and don't speak any languages except English – yet just because I'm cashew-coloured, I'm often questioned about my heritage. Over the last five years, I've been asked: "What's your caste?" (I haven't broken any bones); "Do you go to temple?" (only on my way to Embankment); and "Do you need special food?" (as though the answer's going to be: "Yes, St Peter isn't going to let me in if I've munched on a bit of dead pig/cow/giraffe").

It's not that I'm embarrassed about my ethnic background. I don't think about it much, though it's good for jokes ("I'm half Iranian, half American – so basically, I hate myself"). But some people seem to want me to think about it. "Why don't you visit Bombay?" they enthuse. "You'd love it." They may be right, but have yet to explain to me why I'd love it more than Tokyo, or Guatemala, or any of the other places I haven't yet been. It's an odd misconception that you should somehow feel connected to a far-flung country because your ancestors lived there centuries ago, even if your entire life has been spent morris dancing in Loughborough.

It's not that I think the questioners are all differently faced versions of Nick Griffin, either. I don't – they're probably just curious (except perhaps for the bloke who made a constipated noise when I told him my Dad was white). People with a different appearance often seem more interesting than those who look everyday, and questioners are clearly hoping for a more satisfying response than the mundane "Right here". When they don't receive one, they probe.

So my reluctance to enter The Conversation isn't due to shame or to fear of any dubious ulterior motives. It's partly down to exasperation at people thinking I'm less British than them because I'm brown; but it's mainly down to extreme boredom. The rundown of my convoluted four-continent-spanning genealogy takes ages unless I lie, and I've started to deliver it in a funereal voice more monotonous than Tiger Woods's public apology.

Luckily, I've come up with a solution (one that could work for anyone in this situation, though you'll have to write your own version). I'm going to print out large business cards, and the next time anyone tries to initiate The Conversation and doesn't accept "London" as the answer, I shall furnish them with the following:

"Hello! You may be surprised to learn that I have been asked this question before. Never fear: you shall have your explanation shortly. (Would you like to buy a TV by the way? I have one for sale; 24in screen, Samsung, five years old. Bit flickery, to be honest.)

Right, are you sitting comfortably? Armchair? Cup of tea? Eccles cake? Then here goes: My maternal ancestors are Parsi Zoroastrians (I'm not making this up) and hail from sunny Iran, currently home to uranium obsessives. Between AD700 and AD1000 the Parsis left Persia, as it was then called (I don't know the precise date, they didn't leave a note), and travelled to India. They stayed there for around a thousand years before getting a bit bored again (are you bored yet? I am, but then I'm quite familiar with this story) and upping sticks for East Africa in the early 1900s. My grandad was a builder, though later he imported unfashionable jumpers from Nairobi featuring large pictures of sheep. They were the bane of my life in the playground, I can tell you.

In 1966, lured by the fine climate and that lovely Enoch Powell, my mother's family moved to Britain and have been here ever since. They speak English and everything. Sadly I can't say the same for my father's family, who are all white Americans and live in the States. He moved here in 1970 and met my mother in London in 1978, though declined to apply for British citizenship. Do you know, this means I'm allowed to vote in US elections even though I've never been there? It sounds glamorous, but in 2008 I ended up voting for Barack Obama by fax in Printax Stationers in Clapham, which wasn't very exciting.

So, that's the answer you were after.

But me? I'm from London."