People - what use could they possibly be?

The new proposals on citizenship have kicked off the usual well-informed and dispassionate debate about immigration and integration. Perhaps the bizarrest response was Frank Field's, in which he seemed to assert that the UK has all the people it's going to need for the next 25 years, so we can stop letting any more in now:

It is the growth in population that is the major challenge.
The UK population will, on the government's own estimates, grow to more than 70 million in less than a quarter of a century. Seventy per cent of this growth will be due to migration. This increase of 7 million is equivalent to the building of seven new Birminghams

Now, I admit, at first glance that sounds pretty bad. Seven new Birminghams? Isn't that over-egging the pudding just a little? But consider this - these new Birminghams will be populated by people who are not Brummies. Given our apparent concern over citizens who don't speak English properly, these new-fangled Birminghams already represent clear progress.

Impenetrable accent aside, just what does Frank hold against Birmingham? What's so horrifying about the prospect of more of them? It's a large, thriving city, the third best place in the UK to start a business, the fourth-most visited city by foreign visitors and, apparently, the 55th best city to live in in the world. (He said, carefully maintaining his poker face.)

Throughout his article, Frank proceeds from the assumption that, somehow or other, if we let in too many people, Britain will be imperilled and/or impoverished. Or something. He doesn't present any justification for thinking this, nor does he spell out exactly what these negative consequences are. He just takes it as read that the last thing Britain can afford is any kind of population growth - particularly if it's driven by immigration. Now, for all I know, this may be true. But it may equally be unfounded, knee-jerk parochialism. Without more of an argument, it's difficult to tell.

One of his underlying arguments might be (and I'm guessing here) that too rapid population growth will stretch our resources, and effectively impoverish us all. After all, if population growth outstrips the performance of the economy, we can only end up worse off. Happily, Frank has given us some figures to help us work out how likely this is. The UK population is currently 61 million. In "less than quarter of a century" it will be "over 70 million." Assuming that "less than quarter of a century" means "24 years" and that "over 70 million" means "71 million", this handy Compound Annual Growth Calculator tells us that under this nightmare scenario, the UK population is going to grow by - brace yourselves - 0.63% a year.

I know, I know! An unnerving prospect that ought to strike panic into the heart of every man, woman and child across this fair land. But stiffen that upper-lip for a second like the true-bred Brit you are, or aspire to be, and consider what this implies for Frank Field's argument. He genuinely believes that over the next 25 years, Britain's GDP will be virtually stagnant; that this apparent economic underperformance will in no way affect the number of people who wish to come to live in this country; that GDP will grow faster with a static population than a rising one; that new citizens can only be a net drain on GDP. Either that, or he's not really thought about what he's saying.