> Why can't the UK have open borders to skilled immigrants and not so open to unskilled immigrants?

You would have the extra friction of proving to the UK government that you are skilled. There would probably be a requirement for formal education, so self-taught programmers are in trouble.

I admit I am speaking in my own interest here, as a Swedish person living and working in the UK. When I got a job here I just packed up my stuff and moved. I showed my passport to the border machine and that was it.

If I needed a skilled worker visa, I would probably have had to pay a certified translator to translate my diploma, send in both translation and original, and hope they send them back. Do the same thing for a dozen other documents. The employer would need to submit something, which may be fine for Google but harder for a startup. Then wait for months, because the home office has no incentive to be quick.

Judging by today's discussion with friends one issue is that the UK looks very unwelcoming for immigrants like me now.

We won't make any rash decisions but I think my partner and me are going to leave medium term despite us having great and interesting jobs.

That's not a decision based on economics but on "soft" feelings.

They may leave them open, but for an European engineer it just became a lot less attractive.

They will not want to, but right now those skilled immigrants can easily come here to work, however if there was a lot of visa work to sort out then they may choose Germany or France over the UK. For an employer in London such as google it means dealing with many visa applications from many countries whereas if they were based in frankfurt or Dublin then they just need to deal with visas for UK applicants.

You can't be a member of the EU (or the EAA if i remember) and restrict immigration from other EU countries.

When the UK finally leaves then yes that could be how immigration is managed.