James Cartlidge is MP for South Suffolk.

It was reassuring to read in the Article 50 White Paper that MPs will have a chance to vote on new immigration legislation arising from Brexit. There is one particular question we will need to be asking during the debate that will follow from it: should Brexit globalise immigration to the UK?

As I pointed out during debate on the Article 50 Bill, the heart of the matter concerns existing arrangements for so-called ‘unskilled’ immigration. At this moment in time, it is illegal for ‘unskilled’ migrants to come to the UK from outside the EU. Tier 3, the unskilled route from outside it, has never been opened because, as Jacqui Smith told the Commons in  2008: “We have closed off tier 3 of the points-based system to reflect the impact of inter-EU migration”. In other words, we get sufficient unskilled migrant workers from the EU.

Two caveats. First, in this context the term ‘unskilled’ does not purely mean menial labour. In its immigration policy context, ‘unskilled’ refers to the status of an immigrant whose qualifications and professional circumstances may actually be vital to the country, but who under current law is not entitled to enter the UK to work under the points based tier system for non-EU migrants. This category can include genuinely skilled migrants, and many thousands of workers who possibly are ‘unskilled’ but whom we rely on to keep the country going: care home nurses; sandwich packers; cleaners; hospitality staff; recyclers and meat processers. Overall, the Financial Times has estimated that two thirds of recent EU migrants would not qualify under non-EU visa rules. I am therefore writing about the bulk of arrivals, and that is significant to remember.

My second caveat is that I am a great admirer of those who come from far and wide to conduct often low-paid work in this country, keeping our factories, farms and recycling plants going: not scroungers, but grafters. Nevertheless, I entirely accept that immigration needs to be put on a sustainable footing. As far as I am concerned, my interpretation of the Brexit vote was not just that the public wants to control EU immigration. Rather the message from the doorstep was that the public at large wants to reduce all immigration to the UK significantly.

Yet our current ‘uncontrolled’ system has one significant restriction that seems to have been overlooked. We are restricting unskilled migration to the UK to a potential population of 750 million, rather than opening it to a global figure of ten times that number.

Many on the Leave side justifiably regard this position as discrimination which is only lawful because of our EU membership. The official Leave campaign in the referendum promised to have a single immigration system – thus removing ‘discrimination’ against non-EU migrants. My colleague John Baron said during the Article 50 Bill debate: “by leaving the EU, we will no longer discriminate against the rest of the world, which the present immigration policy does…it is a fact that we cannot stop anybody coming in from Europe, but that we do stop the rest of the world coming into the UK”.

Harsimrat Kaur, a Leave campaigner , wrote recently on this site of the unfairness against non-EU migrants and said that: “post-Brexit Britain should take a global approach to immigration”. And who can have failed to notice all the recent clamour for better visa entry terms for Commonwealth visitors to the UK? Or the indications that trade deals with the likes of China and India are likely to involve a push for preferential visa access for citizens of their vast populations?

To be fair, the Vote Leave position was that you would have one single system – but no unskilled migration at all. One can surely see how a single system would be practicable with purely skilled immigration. This is because there are inherent restrictions in the skilled tiers that automatically reduce potential numbers to an elite band.

However, is a complete end to unskilled migration realistic? Much of the country is at full labour market capacity due to our welcome success in slashing unemployment. Even with free movement, we have severe recruitment shortages in care homes, construction, hospitality, manufacturing and many other sectors. Yes, we have skilled shortages too (not least doctors), but every visit I make to a factory or workplace suggests to me that to support both skilled foreign workers and local talent we need a labour market supply chain with significant unskilled migrant labour for the time being.

This leads to the crunch point that our whole premise for a ‘hard’ Brexit is that we will leave all the EU structures because otherwise we cannot control immigration. But control does not guarantee lower numbers. My worry is that we will end up simply substituting EU immigration with non-EU. We only need to look at Angela Merkel’s recent experience to see what impact messaging has in global migration. What impact would it have if we legislated to tell the world that unskilled immigration to the UK was once again open to anyone from anywhere – albeit with ‘controls’?

Finally, what of the demand and supply mechanism? At the moment we have a rather quaint, old-fashioned system for unskilled migrant labour – the free market. Whatever we replace it with will inevitably be far more bureaucratic and costly, possibly involving tit-for-tat restrictions on our own free movement to EU nations. Yet the man from the ministry may go to all that trouble only to find that he issues so many ‘exceptional’ quotas (care homes; fruit-pickers etc) that numbers see little change. And quite how his job is made easier by the volume area of his trade – unskilled migration – becoming open to all nations is beyond me, even if new controls are put in place.

So while we do need to find a credible way to cap the current system of free movement, it offers more control than we might credit. This underlines the argument for transitional arrangements that buy time not only to put in place a new system, but also to allow the most important job of all – seriously reforming welfare and education so that we eventually fill our posts with British-educated workers.

Yes, when it comes to trade, Brexit Britain should seek to ‘go global’. But I would be surprised if those voting leave did so to globalise our immigration system.