If the UK is such an unproductive, uncompetitive country that needs to have capital and underpaid workers regularly pumped into it to prevent economic collapse, then in the EU or out of the EU, we're fucked either way.
One thing with our economy, much like say Germany and France, is we’re getting older. Healthcare costs rise, tax revenue goes down (in proportion).
Immigrant workers - for now at least - are net positive. They pay more in tax than they draw in services.
I’d like better protection for their labour. I’m not sure “fuck off” is the answer for that.