In the weeks after the UK government extended its limits on the number of low skilled workers allowed to come to the UK from Bulgaria and Romania, there is evidence piling up from Alabama, USA, to show that immigration helps the local economy, contrary to the assertions of governments.

The new law in Alabama requires migrants to have their papers available to show on request at all times.   If they can’t do this, they are arrested.   Last week a German executive was arrested.   As a consequence, Hispanics are leaving in large numbers. Part of the law was repealed recently, but police officers are still obliged to detain people who are suspected of being in the state illegally. And now the results are being seen.

The large manufacturing base established on the back of immigrant labour is reducing fast:  Honda has the capacity to build 300,000 cars a year having in the state an estimated investment of $1.4 billion. Two of the plant’s workers have now been stopped under the law.

There was a loss of 2,700 construction jobs from September to October – a 3.2% drop. And the drop for the last year is 7%. This is partly the result of Alabama’s construction industry undergoing a huge boom up to 2007 – as exemplified in the manufacturing capacity of Honda. Some readjustment was inevitable. But it is partly because of the said amendment to Alabama’s immigration laws that deters workers and, in turn, depresses industry.

In agriculture the effects are indisputable. Crops are rotting in the fields due to a labour shortage. Farmer Brian Cash was employing 64 people; the day after the law was passed that dropped to 11. Now there isn't one, and the estimated loss of crops to Mr Cash is $100,000.

Alabama’s reasoning for passing this law is much the same as the Home Office’s reasoning for restricting the number of Bulgarian and Romanian workers coming to the UK, and for having the Seasonal Agricultural Workers Scheme – a quota for the number of seasonal unskilled workers that can come to Britain. The apparent idea is that restricting immigration results in more jobs for natives and residents, as per the latest Migration Advisory Committee report. But now Alabama is losing construction work, and tomatoes are rotting on the vine. This in turn will push prices up: both of labour, and of food.

Unemployment is the result of the recession; limiting immigration will not solve that. And the lesson from Alabama is that it might make it worse, for us and for decent salads everywhere.