One of the biggest challenges facing the United Kingdom since the Second World War has been the immigration of the last 20 years.
Mass immigration has in many respects greatly enriched Britain. It has made the country more diverse, and helped make London a plausible contender for the title of greatest city in human history.
Relations between the various communities in that vast metropolis have been mostly harmonious.
Much of the NHS is staffed by dedicated migrant workers. And even in Northern Ireland, on the edge of the UK, we have seen the benefits that can come from migrants, such as the eastern Europeans who have worked hard in a range of jobs.
But there are also huge problems with mass immigration, that are becoming more and more apparent in Great Britain, particularly the southeast of England.
The numbers coming into the UK as a whole have been formidable, with net increases numbering in the low hundreds of thousands of people per year. Millions of immigrants have come into the UK over the last 20 years and most of them have settled in London or the counties that surround it.
This has led to increasing pressure on public services and it has fuelled a house price boom that has pushed property ownership out of the hands of most people aged under 40.
There is a further cultural problem with some Islamic immigrants who refuse to integrate, and in rare but by no means isolated instances this has led to terrorist plotting and activities. There are many reasons for the influx. The Labour government post 1997 encouraged it, but even if not it would have been hard to control. Now some politicians, such as Michael Gove, say continued EU membership will make the situation worse. Critics counter that Leave will barely improve things.
But regardless of who is right on that point, we need cross-party agreement that the UK, with its high population density, is now full, or close to full. This is not a mean or a racist point. It is an increasingly evident statement of fact.