Because there will still remain advantages to living in Britain and the step might be perceived as even more natural that OTL due to it and the sending areas being part of the same meta-country.[/QUOTE
Excellent choice of worlds on Enoch, 'Intellectual mistake' is a most elegant way of putting it, I'll have to remember that.
If what you propose is true then I think your answering your own concern, if the former Dominons/colonies become even more Anglicised there's less culture clash when peoples meet. Moreover I would the issues are not so much racism or even strictly speaking xenophobia, but are more about general outsiders regardless of colour of creed. These problems come to the fore generally when the economy is bad, when people are losing jobs or struggling seeing a group who 'aren't from round here' doing well cause anger. There is a assumption (an incorrect one) that their prosperity has been stolen from the 'natives' and if the outsiders went away the natives could have that prosperity back. It happened in Sweden in the early 1990s is I recall correctly (it's important to remind Swedes their country is a very, very long way from perfect.)
On A) you miss. It's just annoying and somewhat condescending. On B) you misunderstand, the purpose of First Pass the Post is to prevent nutters gaining any power and minimising their influence. It's really a kindness, rather than disenfranchise the alarmingly large number of said nutters we give them a large variety of no-hope parties to vote for so they feel involved but can't do any real damage.
It is this system, together with proper beer and the a proper Breakfast that gave Britain the greatest Empire the world has ever known and produced TV, electricity, modern sewerage systems, the jet engine, hovercraft, railways, transatlantic airliners, the package holiday, the world wide web and most of the world's sports.
Sweden with its sweet beer, continental breakfast (a ham and cheese sandwich in reality) and proportional representation produced none of these things. Instead it gave the world mass produced matchsticks, the Volvo, the world's most ironic prize (the Nobel Peace Prize), an inferior form of explosives and suicide.
I think you'll agree the first list was superior in almost every regard to the second list.
Progress! We'll beat that Swedish soft left socialism out of you yet.