One of the many justifications offered by advocates of Brexit is that it will allow the UK to "regain control of it's borders". I am doubtful that this is the case; it may do so, but if so it will come at a price.
Following Brexit, should that be the electorate's verdict, supporters and opponents alike will be hoping that the UK's economy continues to grow (as measured by GDP - the sum total of the nation's economic output). For a nation's GDP to grow either the existing workforce needs to become more productive (generate more output, in terms of goods and services, at a lower unit cost) or the workforce needs to grow. In the UK over the last 20 years or so, this demand for more labour has been met by immigration. The UK's unemployment rate currently stands at 5.1%. In such a low unemployment environment if a company wants to expand it's business but access to immigrant labour has been removed it will need to raise wages in order to hire more people - to poach them away from other employers. This may appear superficially attractive, giving workers a pay rise, but in the long run it is bad news. The UK has a long running productivity problem (currently worse than France's), which makes our exports relatively expensive. This has led to us having the worst trade deficit in our history - we import massively more goods and services than we export. If wages rise we become more unproductive and the deficit becomes worse - a situation which in the long run is not sustainable.
So, post-Brexit, wages will tend to stabilise at a level at which our productivity does not worsen and as a nation we are able to continue to compete. Competition for employment is what constrains wage growth - when we no longer have immigration to provide that competition it will be provided instead by an increase in unemployment. The market will drive up our productivity through the mechanism of falling exports leading to higher unemployment. The final result of a Brexit followed by closing the borders will be a shrinking GDP, falling wages and higher unemployment. That increase in unemployment has associated welfare costs which will have to come out of a smaller tax take due to the smaller size of our economy.
Overall post-Brexit Britain is not an attractive prospect, which is why I think those who vote for Brexit in order to reduce immigration will find themselves disappointed. No government wants to preside over a shrinking economy, permanent recession and falling living standards - for this reason I believe Governments will continue to listen to the demands of business and the borders will remain open. Globally, mass immigration is here to stay and our time would be better spent in finding ways to live with it.