Yes i find it interesting too
. I'll try and answer your questions as best as i can
In terms of the British women appearing desperate, i think it may have something to do with the types of British women who tend to date "Freshies." I have noticed (and i don't mean to sound bitchy/judgemental) that a lot of the British women who go for them, tend to be considered unattractive, which is perhaps why this reputation of desperation comes from-as a lot of people tend to say that the only British women who go for Asian or African born men are those who cannot get a British man. I agree that there is also the element of the man in question appearing desperate for a visa-but as i said before this only serves to make the woman look even more desperate as some would take the piss out of her for either ignoring or not realising that he could only be dating her for a visa (when the woman in case is unattractive, this only confounds people's suspicions that she is being used.) People may also take the mick because Asian and African born men tend to be seen as lower in the social scale than British born people (most likely due to them doing low paid work and also negative stereotypes about their countries of origin being poor etc.)
As far as sleazy and culturally backwards things go-it's mainly stuff like chatting up much younger girls etc. It's not rare (at least in Birmingham) to see Asian born men especially (and age wise i'm talking guys who look like they're in their 30s) to chat up girls who are 14/15. For example, i remember when i was about 14 there was an Asian guy (Pakistani i think rather than Indian) who run the chip shop who used to try and get me and my friend's numbers in exchange for free food/drink. And there was another guy (who i think must have been in at least his 40s) who used to buy my friend alcohol if she flirted with him. Now i'm not say that this type of behaviour doesn't happen amongst British men, because it does (and i'm not saying that in some cases young girls don't encourage it in exchange for money/alcohol/fags etc), but this kind of behaviour does seem to be more common amongst guys born in Asia. It's like they have no concept of age or anything-which is seen as unacceptable in this country.
You're right, Birmingham is a very multi ethic city, but (unlike London) it doesn't have as many economic opportunities for immigrants so whereas it seems in London a lot of guys from India etc work in finance-in Birmingham most of them tend to work in low paid work (e.g. factory work etc) and also tend (from what i've noticed anyway) to work in places owned by Indian people, and with a workforce mainly of fellow Indian born people, so "non Freshies" don't really get a chance to mix with "Freshies" in the same way that maybe you guys in London do. (Obviously there are Indian Doctors etc, but your average Brummie isn't a Doctor lol, so thus don't get to mix with them in a non professional setting.) British born people in Birmingham tend to mix quite well (although there is some segregation between those of different races) but non British born people (and i don't only mean Asians or Africans, but also Eastern Europeans for example) do tend to socialise mainly amongst their own communities so there isn't really the amount of mixing that you would expect in such a multi cultural city. Because of the little interaction between British people (especially White British people) and Indian born people (for example), there does tend to be some ignorance about accents/clothing etc-which is maybe why "Freshies" get such a bad rep.
I wouldn't say that it's as culturally insensitive today for a non White guy to marry/date a White female as it was in the past (for example as it was when my nan married my grandad and her family disowned here lol)-although obviously there is still some ignorance regarding it (i've got a friend whose Dad would disown her if she married a "coloured" man.) I'd say (possibly due to events like 9/11, 7/7) the main "taboo" would be males of a Muslim background (particularly Pakistani) dating a White woman, as although it happens-the girl in question would probably get a lot more negative comments than if she were dating an Indian or Black guy (i knew, for example, a mixed race Black and White girl who fancied a british Pakistani guy but her dad-who was Black-basically told her that she couldn't date him, and i've heard girls get called stuff like "Paki Bashers" if they date a Pakistani guy.)
I think it does all boil down to some sort of cultural ignorance, as well as (sometimes unfounded) negative stereotypes about Asian or African men (i should say, btw, that the reason why i've focussed more on Asian men rather than African men, is that while stereotypes do exist concerning African men, Birmingham has WAY more Asian born men so therefore i know more about them, whereas i've only properly met about 3 or 4 African guys.)