Wikipedia has a pretty good, thoughtful article on this subject. I found the sections on "Sensitivty to Pain" and "Cultural Beliefs" informative.
When, a year or two back, I had to be tested for hereditary haemochromatosis, I looked into the genetics of "bronze diabetes", I remember reading that it was postulated that the genetic mutations that produced both HHC and red hair originated in the British Isles (no offense to Irish readers, but this means Great Britain, Ireland, and the thousand or so smaller surrounding islands) in the first place.
So, firstly, it's worth mentioning that red hair is statistically the most common not in Ireland, but in Lowland Scotland. As such, the British Isles generally, and the UK in particular, are probably the only place in the world where redheads are common enough to appear to be a distinct sub-group, rather than just a curiosity.
It is no surprise, therefore, that if there was going to be any persecution or prejudice against "gingers" (typically pronounced here with a hard "g", like in "gingham", and rhyming with "ringers", when used pejoratively) anywhere on the planet, that the UK was the first or most extreme place it was going to happen.
1. What causes this prejudice against red hair in the UK?- Most simply, higher levels of occurrence
- If theories on pain thresholds, as mentioned in the Wikipedia article I linked to, hold any water, then maybe red heads got a reputation for complaining more in the face of the normal bumps and grazes of life - nobody likes a whinger (which, in modern British English at least, rhymes with the normal pronounciation of "ginger").
- At a much deeper level, I think that the British can be the nastiest, pettiest, meanest, surliest, most casually vindictive and brutal people in the world*. It is a source of continual, and pleasant, surprise to me that while we can be that horrible to one another, most of the time our (self-described, it has to be said) reputation for tolerance and fair play wins out and we aren't constantly tearing chunks from one another (both literally and figuratively). Indeed, I'd say that most of the reason for our national self-description (or self-delusion) of tolerance is not because of any absolute level of tolerance, but that we are comparing ourselves to how bad we (mostly subconsciously) know we could be.
This manifests itself in any number of ways, but most particularly, there is a strong element of what we call "mickey-taking" (from ancient rhyming slang for a urinary profanity) in the national psyche; the much mythologised British self-deprecating sense of humour arises mostly, IMO, from a need to make a joke of our own shortcomings before someone else does, so at least we retain control. What is now called bullying is endemic (read Tom Brown's Schooldays; hell, even Henry IV in the Shakespeare plays spends most of his youth carousing and being the butt, and the maker of jokes, few of which are very kind. Indeed, if anything has changed in recent times, it is that something which used to be tolerated or even celebrated as some kind of rite of passage has become frowned upon (rightly so), and wider British culture has yet to catch up.
So, especially among the young (say ages 8-25), any difference is quite mercilessly lampooned by those whose minds turn to *** NOTICE: THIS WORD IS AGAINST THE RULES. FAILURE TO REMOVE IT WILL RESULT IN A STRIKE. ***-taking (which is most Brits), and mercilessly beaten by those that prefer violent expressions of their hostility (a smaller minority, thankfully). It doesn't matter if this difference is red hair, brown skin, thick glasses, acne, speech or accent differences, body shape, sexual oreintation or football club supported; sooner or later almost every British child, teenager or youth will find themselves the object of cruel amusement, and some will find that it escalates to violence.
I say this with no sense of national pride beyond it is a deeply ingrained part of the British sensibility, and without it we would be a different people (better or worse is not for me to say - I suspect neither, just different).
* In defence of this, I refer to an apocryphal pamphlet given to US servicemen stationed in the UK during WWII which went something like
do not confuse the British people's reserved and laid back demeanor for timidity or weakness. The British did not build the largest land empire in the history of the world, or dominate the seas for the better part of two centuries, by being unable or unwilling to stand up for themselves, or to take what they want by force without fear of the consequences. I paraphrase, but the gist is that the British are not nearly as nice as we pretend to be, to ourselves and to others.
2. How serious a problem is this?For British redheads, very, but I think (as outlined in my last point above) it's a mistake to think that redheads are being singled out for hatred. It's more that there are a disproportionate number of Britons who want or need to hate something or someone, and red heads are a handy scapegoat if they wander by at the time.
3. Does it tell us anything about other forms of prejudice?Yes. Prejudice is very deeply rooted and the point of apparent difference that the bigoted fixate on is pretty much immaterial. If we were to have a discussion on why racism against and by black people is still practised so widely in America, and why it so often spirals into violence, where (comparatively) it doesn't in the UK, we'd have a whole bunch of posts delving into the details of this statistic or that occurence - as we often do here at

- which ignores the basic principle that black people are, through no original fault of their own, the main faultline in America society in a way they just aren't in the UK. Our intolerance doesn't have such a potent and attractive lightning rod, so while no less potent or attractive, bigotry and intolerance in the UK are more diffuse. (This isn't quite true - the faultline in the UK is still the class system, but this has crumbled since WWII, again causing our inbuilt store of nastiness to lose focus and become more diffuse.)
4. Does my hypothetical model of one source of prejudice (visible signs of historical oppression leading to feelings of guilt, leading to feelings of resentment) make any sense? Not really. I think it's more simply just suspicion and dislike of difference.
Despite it's relatively small size, Britain was historically a very insular place - many generations would grow, live and die in a single place, where even the county town was a far-off and exotic place only spoken of by others. People only started moving around the country in large numbers in the Industrial Revoluton.
To this extent, English peasants would hear stories of strange, wild people with red hair living in the mountainous areas of the UK but would have no more reason to hate or fear them than the people with no heads and faces in their chests, or people with two heads, that came back from forever-embellished, second- and third-hand travellers' tales.
The other flaw I see in your hypothesis is that guilt at past treatment of a particular ethnic group (the Celts, formet African Slaves, the Jews) is a pretty modern (late 19th Century at the earliest) phenomenon. The oppression of the Celts
as a race was already very old by this time - ancient history to anyone alive; so there was too much of a generational disconnect between the perpetrators of anything really horrible and people alive at an enlightened-enough time to think it was bad.
Plus, in the Dark Ages, Medieval and early modern period (from when the Romans left to the Industrial Revolution) when most of this oppression (of Celts) was going on, the feudal and class systems were so rigid that there was no sense among the English that is was "us" doing good or bad things to "them". The kings, the lords and their armies may well have been doing those things, but the great majority were serfs or peasants or what-have-you who were every bit as oppressed as the poor Celts, albeit in different ways. (Thinking about it, I'm sure this is where the ingrained habit of nastiness comes from - when you've been treated so badly for so long, your culture changes to permit you to vent at anyone different. The societal equivalent of the henpecked husband kicking the cat, perhaps?)
Lastly, in the British context, while it is now common to accept a share of responsibility for the ill-treatment of colonial subjects, or of Jews, the Irish, or the descendent of African slaves, the English have not yet indicated any remorse for their subjugation and oppression of the Scots or the Welsh (on whom the English practiced all their worst and best habits of colonialism). Neither do the Scots or Welsh lay any particular claim to reparations or even think of themselves as victims of anything much, save perhaps linguistic oppression (which, continuing as it did into the early 20th century, is still culturally recent). It's all a bit too long ago, and too much has happened in the interim (the Celtic nations formed a significant part of later imperial adventures - and atrocities - overseas. Anyone seen
Zulu?).
edited for mild profanity, and to add that it appears
moif and I share more or less the same perception of the default settings of the British people.
Put it this way, if
Bambi had been a British animation, there is
no way in the world that Thumper's dad would have said "If you can't say anything nice, don't say anything at all". Unless it was immediately followed by a vitriolic put-down, or by (literally) cartoonish violence, perhaps with a pay-off line of "Oh shut up" from the fox that ate him/farmer that shot him/car that ran him over. That sentiment simply does not exist in the British national psyche, except perhaps in the wimpier parts of the whining soft left. (You can tell from my less-than-positive epithets that it's not a sentiment I share either.)