A lot has changed in Poland trough past couple years especially for developers. You can now get decent salary in major cities. It's still not as good as in UK where you can have decent salary in cities with population of 30k+ but it's getting there, plus there is always Germany witch is close enough.

Quick story. I am working for small UK holidays company located in one of the biggest IT hubs outside of London. Our whole dev team is made up from non UK, EU citizens. Recently we had openings for mid backend dev and junior/mid frontend dev roles and only about 20% of CVs was from native UK citizens (mostly, highly under qualified even for junior role/couldn't pass FizzBuzz). Rest of candidates was mix of EU, visas and double citizenship and we ended up offering both positions to two EU citizens.

If UK government will ban employment of people from outside of UK or make it difficult or expensive then small companies like ours will not be able to operate.

I see that developers are looking more and more for jobs outside of the UK. Recruiters and EU employers also can see what is going on and I'm receiving more job offers from them, offering help with relocation outside of UK.

There are some decent companies on the tech area. Poland is one of the "cheap" EU countries with decent workers, that's a good reason to have a big office there.