Well, for starters the working classes highly resented that the EU mainly benefits the corporatists, banksters, and other assorted elites and bureaucrats. Sound familiar?
And it's just a fact that the EU was sold as a simple trade organization that has grown into a large undemocratic political organization with strong hints that an EU military is to follow.
Xenophobia absolutely played a part in it, but don't forget that people vote in their own self-interest.
The working class resents the fact that the British are told by the EU how many benefits migrants are owed upon arrival in Britain. This is one of the issues that Cameron has supposedly "negotiated."
The working class resents the crowded schools and overworked National Health Service brought about by an influx of immigrants (and a conservative government).
They resent numerous little things that we don't think about.
The working class resents that migrants can qualify for council (government) housing, while they remain on a wait list.
And the middle class resents that they can no longer get their foot on the bottom rung of the housing ladder due to a severe housing shortage.
The list of resentments against the EU is long! This is not just about xenophobia. While Labour party leaders were pro remain, labour party members voted leave!
I'm afraid that the EU just doesn't have the appeal to the working classes that it does to the upper middle class. Everyone I know in Britain (I lived in England) was hoping to retire in a little village in France or Spain, or even in one of the poorer EU countries where their pensions would have gained them a higher quality of life. Even if they never left, it was always going to be a dream.
The working classes can't afford to up and move. They won't have proceeds from the sale of their house to buy them a "little cottage" in the French countryside. They see no reason for borders to remain open. They aren't going out; all they see are more people coming in. They don't care if they will have to stand in line at border control; they can't afford to travel, anyway.
These are not petty issues and they are multiplied many times over
what I could type.
And, again, they resent the ridiculous bureaucracy of the EU.
"The EU is poised to ban high-powered appliances such as kettles, toasters, hair-dryers within months of Britain’s referendum vote, despite senior officials admitting the plan has brought them “ridicule”.
http://www.telegraph.co.uk/news/2016/05/10/eu-to-launch-kettle-and-toaster-crackdown-after-brexit-vote2/
The bureaucrats in the EU can't help themselves. Even with the Brexit vote poised to take place, they were continuing to show how out of touch and petty they have become.
If this is a divorce, the EU did much to provoke it, and now they've got to figure out how to break up while still maintaining the peace for this millennia.