In the UK, October is Black History Month, and my local library has an interesting display of records showing that there were black people (those of Afro-Caribbean origins) in Hertfordshire as far back as the sixteenth century, mainly slaves or freed slaves. But if you go further back, into the Middle Ages, "black" becomes a more slippery concept: how do you decide who to include and on what basis? So instead, I want to talk about my own history. In particular, I want to tackle a claim that's often made about middle-class liberals like myself: that we're only positive about immigrants, immigration and ethnic minorities because we're unaffected by them ourselves. We're actually living in ivory-white towers or at least suburbs. I saw this suggested on the American political website Obsidian Wings a few months ago, when they were discussing a map displaying ethnic diversity in the US.

I haven't got access to anything like this for the UK. What I'm using instead is statistics for the smallest areas I'm able to find, taken from the Neighbourhood Statistics website for England and Wales (Scotland has separate statistics). These go down to electoral ward level, the smallest electoral unit, which cover on average a few thousand people. I've listed below figures for the absolute numbers and proportion of white people and ethnic minorities for all the places where I lived for more than a few weeks.

A couple of notes on the data. Firstly, this is all taken from the census results of 2011, whereas I was living in some of these places more than forty years ago. So the exact proportion of ethnic minorities may have changed, and is likely to have increased from when I was there. Secondly, I have lumped together all people describing themselves as "white", whatever their sub-category (i.e. including those who are not native to the UK), and compared them to those from any other ethnic group. With those caveats, here is my black history

1) (BN18 0NJ/BN180RE) Walberton ward (West Sussex) 2829/2889 white; 2.1 % ethnic minority
This is where I grew up in rural Sussex, and I suspect it was more like 0.1% ethnic minority back in the 1960s and 1970s.

2) (OX2 6HS) Oxford North 4921/5809 white; 15.3% ethnic minority
St Anne's College, Oxford: the statistics are probably affected by the high student population.

3) (OX14 2AJ) Abingdon Northcourt 4572/4835 white; 5.4% ethnic minority
Where I was living during my first job.

4) (SY23 3AL) Llanbadarn Fawr-Padarn (Aberystwyth) 958/1042 white; 8.1% ethnic minority
I attended the College of Librarianship Wales here: again, the statistics probably reflect the student population as much as the locals in deepest, darkest Wales.

5) (GU14 9AQ) Mayfield (Farnborough) 5086/6635 white; 23.3% ethnic minority
Location of my first job as a professional librarian, in 1988

6) (PL4 7HU) Efford & Lipson (Plymouth) 13575/14092 white; 3.7% ethnic minority
Where I moved to when I got married.

For comparison, my husband was also brought up in a very white rural area: (BS18 7HP) Blagdon & Churchill (Somerset) 3732/3815 white; 2.2% ethnic minority

7) (SN3 2RG) Parks (Swindon) 8868/10281 white; 13.7% ethnic minority
Probably the poorest area in which we've ever lived during our marriage, but by no means the most ethnically diverse.

8) (SN3 6NF) Dorcan (Swindon) 7786/8684 white; 10.3% ethnic minority
This was where we bought our first house in around 1992.

9) (GL1 4AA) Barton & Tredworth (Gloucester) 6419/10953 white; 41.4% ethnic minority
The first place I lived where I regularly saw women wearing the niqab.

10) (Westmoreland Road, Bromley): Bromley Shortlands 8288/9824 white; 15.6% ethnic minority

11) (AL1 5LL) Ashley (St Albans) 6366/7892 white; 19.3% ethnic minority

12) Hitchin Bearton Ward 6730/8489 white; 20.7% ethnic minority
The location of our current house.

Obviously, such an overview can't convey all the details of my experience: I've lived in some areas (such as Hitchin) for much longer than others and in some areas I was working fulltime and actually didn't see much of my neighbourhood. But as you can see, it's certainly not the case that I've just lived in "nice white areas".

What interests me more, however, is using these figures to think about thresholds and the effects of perception. Hitchin, unlike some UK towns, is relatively ethnically mixed: the statistics for the four other wards into which the town is divided are:

Hitchin Highbury (SE of town) 6914/7762 white; 10.9% ethnic minority
Hitchin Oughton (Westmill estate) 4222/5085 white; 17.0% ethnic minority
Hitchin Priory (SW of town) 4073/4388 white; 7.2% ethnic minority
Hitchin Walsworth (E of town) 6486/7877 white; 17.7% ethnic minority

If I was walking around Hitchin, I don't think I could easily tell the difference between an area with a 7% ethnic minority population and one with 20% of the population from an ethnic minority. That's a difference that I'd need to be counting quite carefully to notice. And thinking back over the places I've lived, I find it hard to distinguish between more than three categories: very white (West Sussex, Plymouth), very high minority population (Gloucester) and ethnically mixed (the rest).

There is definitely some kind of threshold between when it's rare to see a non-white face and when it isn't: I suspect there's a change at somewhere about 3-5%. And there is also a threshold where if you're white you might start to perceive yourself as "outnumbered", even if it's not a majority-minority area. My very approximate guess is that it would be somewhere around a third: if several times a month when you come out of your house, you're likely to find the first couple of people you see are visibly different from you, that's noteworthy at first. (One of the other interesting questions is how long it takes before you get habituated to a particular level of ethnic mixing and take it for granted).

Britain is gradually becoming less racially segregated, although it may not necessarily feel like that in some areas. But that's one of the most interesting thing I think we can gain from comparing our own views to that of statistics: our perceptions aren't necessarily accurate. My Black History is, and always will be, a rather different experience from anyone else's Black History.