The year is 2035. Prime minister Nigel Farage’s hard-right coalition government has reduced net immigration to a trickle. Most people credit rigid quotas and ICE-style repatriation policies. Working with president Marine Le Pen of France, the British have also stopped the not-so-small boats carrying asylum seekers across the Channel. On the surface, everything is going to plan.

But appearances deceive. Britain’s “indigenous” population is static and ageing. There are increasing reports of staff shortages in hospitals and social care homes. The City of London – once a magnet for banking talent from around the world – is complaining about a shortage of cleaners in Canary Wharf and a dearth of quant traders from France and Italy. Restaurants cannot find waiters. Jay Rayner, the celebrated food critic, has just proclaimed the death of the two-seating system for the nation’s top eateries.

I could go on with this playful fantasy about the future, but let’s return to today’s hard reality. The UK needs immigrants. The demographics point one way. We may not be in as dire straits as Japan, South Korea or, for that matter, China, where the cost of the coercive and deeply misguided one-child policy has come due. But in the absence of immigration, the relatively low birth “replacement” rate means that the total number of people living in the UK will shrink, as projected by the Office for National Statistics.