I think people blame 'Brexit' for racism in the UK. I think this is quite unfair. Right-wing, nationalistic politics are on the rise world wide (especially in Europe). Trump became president on the back of a pledge to 'build a wall'.
This article gives a good overview: https://www.bbc.co.uk/news/world-europe-36130006
This shows there are wider causes, which trigger racism.
Look at German Cities like Cologne where there have been riots because of the increase in refugees. I think Germans are very welcoming, but there is that underlying racism in every country.
I think these racists have used Brexit as a vehicle to normalise their hate. We shouldn't blame Brexit for racism, we should look at why this trend is emerging on a global scale and think of new approaches to tackle racism. If EU citizens like yourself are being deported after Brexit, it will be a travesty and will only incite further racism. I'm hoping for a Brexit that leads to controlled and sensible immigration, new trade relations and opportunities. There's no reason why Britain has to alienate itself from Europe, but there should also be no reason why Britain can't trade freely with any country of our choosing. Brexit should be about the wider world.
Brexit seems to have made the expression of racism "salonfaehig", to borrow a term from my native language, ie it's become acceptable to express these views without fearing much repercussion (if any). My Polish and Romanian friends who suffered racist abuse had been in the country for sometimes decades without feeling unwelcome. That has now changed and is driving lots of them back "home". Statistics suggest that hate crimes are noticeably up. And I agree that racism needs tackling.
I'm unaware of "riots" in Cologne (there's been mass-groping of women, which has been instrumentalised by all kinds of global rightwingers...). I think the latest numbers I've seen suggest that 25% of Germans have a "migration background" - either they or one of their parents were not born in Germany, so yeah, pretty mixed and pretty welcoming.
Regarding "free trade" - the EU has all manner of trade agreements with all manner of countries and the network keeps growing. If Britain does crash out, it loses those trade agreements, and it'll take decades to put them back in place. Meanwhile, trade does have to do with distance, ie trade with your closest neighbours is generally more important and plentiful than with nations further away, that's just the logic of economics. I'm generally in favour of lower trade barriers, but the EU is doing a pretty good job at protecting those who cannot compete with others globally because those standards are lower (farmers, for example, who spend extra on animal welfare might not be able to compete on price alone with farmers who abuse animals). And trade barriers are generally coming down all over the world, so if you want to globalise trade even more, why not work inside a structure like the EU which has a totally different weight and power than any one country on its own?
The UK has always been in control of immigration, but chose to not enforce the rules it did have. Also, if it had, I wouldn't be here because it took me a couple of months to get a job (I took the first one I could - university grad working minimum wage data entry, but it didn't hurt me much...).
And the alienation has already happened - the UK's policy regarding Europe has - for centuries - been to keep a nice wedge between France and Germany, but those two are now closer than ever and that has potentially wide-ranging consequences. For somebody interested in history, it's fascinating.