EU referendum Leave campaigners have called for an Australian-style points-based system for all migrants entering the UK, saying it would be a "fairer" system for Britain.
But the Remain campaign said the idea - which would accept people like skilled workers or wealthy entrepreneurs - would actually drive up immigration.
Immigration has been centre-stage throughout the campaign, but with both sides making extreme accusations and opposing claims, these eight facts are what you need to know to settle any 'Brexit' immigration argument.
Currently, the points-style system that Leave campaigners have called for is only applied to people immigrating from outside the EU.
But the think tank Migration Watch has said this approach would be "totally unsuitable" for the UK because Australia is trying to increase its population through "growth by immigration" - quite the opposite of the UK.
A press release from Migration Watch in 2014 said: "The Australian context could hardly be more different. Many Australians believe that they have a strategic need to grow and have the space to do so. Both major parties [in the country] favour increased legal migration and their PBS is a means to that end... Furthermore, net immigration to Australia is proportionately three times higher than ours as the Australian Government pursue their strategy of population growth through immigration."
The Telegraph claimed on 12 May that ONS data showed an "extra" 1.5 million EU migrants came to Britain over last five years without counting among official statistics. Immigration estimates in February suggested around 257,000 EU nationals migrated to the UK in the year to September 2015. Yet 655,000 National Insurance (NI) numbers were issued to EU nationals looking to work or claim benefits in the UK over the same period.
Full Fact says the difference can be explained by the fact that the ONS only counts someone as an immigrant if they intend to stay longer than a year, in line with a UN definition. If they intend to stay for a shorter time they are counted as a short-term immigrant or visitor. This doesn't prove there are 'extra' hidden migrants, Full Fact argues.
And that has always been the case, according to Full Fact. But the gap is closing: the number of EU migrants has soared while non-EU migrants has fallen. The most recent figures put net migration from EU countries at 184,000 a year and non-EU just above at 188,000.
Regis Duvignau / Reuters
EU-only net migration was 184,000 in 2015, equalling its record high. David Cameron had promised to bring net migration down to below 100,000.
The Government has said it wants net migration to be in the “tens of thousands” - rather than the record high of 333,000 in 2015. Some experts say Brexit would make little difference to reaching this target, given that the recent figures put net migration of non-EU citizens at 188,000. According to the Migration Observatory, an impartial research group at the University of Oxford, even if we left the European Union - assuming we kept the current economic conditions and policies - "Brexit alone would not sufficient to bring the target within reach."
The vast majority of EU migrants in 2015 said they were coming to the UK for work - and 41% said they already had a job arranged. By contrast, most non-EU migrants (47%) say they have come to study, according to Full Fact.
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"Probably the greatest challenge in assessing the impacts of EU exit on migration is the fact that we do not yet know what kind of relationship would replace EU membership," writes an expert for the UK in a Changing Europe Initiative, an impartial project based at King’s College London.
"On the one hand, it is possible that the UK’s membership of the EU would be replaced by an association agreement of some kind that included free movement," the post reads. "Norway and Switzerland, for example, have both implemented free movement as part of their economic cooperation agreements with the EU. If this happened in the UK, the impacts of Brexit on UK migration could be relatively limited.
"On the other hand, EU withdrawal could mean the end of free movement and the introduction of admission requirements for EU citizens who want to live and work in the UK. These could take various forms, but the most obvious scenario is that EU citizens would face the same rules as non-EU citizens."
The Sun/PA Wire
If the UK votes to leave the EU, a major consideration would be whether we could remain in the single market - something some economists consider essential to our prosperity. Non-partisan think tank Open Europe says that having some kind of free trade agreement with the EU would be "vital" in the event of Brexit. It argues that the example of Norway and Switzerland - which are not in the EU but have trade arrangements suggest that keeping the principle of EU free movement may be the "price" the UK has to pay to keep our free market arrangement. Switzerland trying to negotiate migrant rules while keeping its trade agreement "without much joy so far," according to the think tank.