If you want to know what Britain will look like after it takes back control, just look to Guernsey’s decline

With the Commons vote won and Article 50 set to be triggered, attention is now turning to the hard negotiations ahead and their impact on future prosperity.

The favoured answer when free movement from the EU ends appears to be tightly controlled schemes which limit foreign workers to short periods in the UK. But any minister who wants to see the wider economic impact of such policies need look no further than Jersey and Guernsey.

The two biggest of the Channel Islands have a great deal in common. Both have their own governments for populations no bigger than a market town. Neither has fully recovered from the effects of the global crisis on their financial sectors. But it is the big differences in their approach to immigration in recent years which should give UK ministers pause for thought.

Guernsey, where I live, has adopted a tough stance. Those coming to work in lower-skilled jobs face very tight restrictions – curbs which are being further toughened. In future, even those who have worked regularly here in the past will find it hard to return.

These tight controls are already having an impact. Figures published last month confirm the island’s population was lower in March 2016 than three years before with net migration over the past 12 months reaching only 121 after three years of being in the red. It is an outcome to delight those pressing for similar controls in the UK.

But the result is that the number of people of working age has fallen and firms are struggling to fill vacancies. Businesses have reduced opening hours and some are being forced to close. New curbs preventing regular workers returning will mean a further loss in skills and experience with the downward spiral looking set to continue.

Jersey may be less than 30 miles away but has adopted a more open approach. There are still restrictions on employment, housing and welfare but the island takes pride in having an immigration policy which is, according to its Chief Minister, “light-touch, pragmatic and delivers the results businesses need”.

Far from pulling up the drawbridge, net migration in 2015, at 1500, was at record levels. This follows three years when it added 1,900 to the island’s population. And this is not just about attracting high-worth individuals or those in the professions.

Jersey has made it easier, too, for those who work hard and progress at whatever level they start to build a life on the island. They see the benefits of encouraging those with drive and talent to stay rather than having to rely on a very transient workforce.

There are many different reasons why economies grow and it is difficult to isolate the impact of particular factors. But there is nothing I have heard or seen which makes me doubt that immigration has helped Jersey’s recent growth outstrip that of its neighbour.

Jersey’s economy has rebounded strongly with GDP growth of two per cent in 2015 following an exceptional four per cent rise – among the very best in Europe – the year before. Guernsey, in comparison, saw its economy grow by 0.4 per cent in 2015 after flat-lining in 2014.

Both islands face major problems including how to fill a worrying shortfall in government revenues. But I believe Jersey has a better chance of overcoming these challenges by encouraging those who can contribute to their economy and island life to stay.

It is a lesson which the UK, as it wrestles with shaping a new immigration policy to balance the needs of the economy and public opinion, should remember. Kicking out those with energy and ambition can make everyone poorer.

Guy Hands is chairman and chief investment officer of Terra Firma