Since the Brexit vote, workers from Europe have been worrying about what's going to happen to them. And it's not just the workers who are frightened. Business leaders and the City of London are concerned about a huge skills shortage if access to the European market is restricted.
A report by accountants PwC put forward the concept of a regional visa system. Mayor Sadiq Khan is backing the idea. But what does this actually mean?
Why does London want its own visa system?
Almost in one in 10 Londoners were born in another EU country — that's around 850,000 people. Compared to the rest of the UK, EU workers fill most of the higher-skilled managerial, technical, and skilled trades jobs in London. It's the openness to talent from outside the UK that's crucial to London's financial success, says Kat Hanna of the Centre for London.
If current immigration rules for non EU citizens were applied to Europeans living here, three quarters wouldn't be given a visa, immigration expert at PwC Julia Onslow-Cole told the first meeting of the London Assembly EU Exit Working Group.
To prevent a skills shortage and maintain its global financial standing, London must have its own immigration controls, the meeting heard.
Do any other cities have visas?
London is not the first city wanting control over the people allowed to stay. Quebec has full power over immigration policy, with separate programmes for entrepreneurs and skilled workers based on their French-speaking skills, education and work history.
This points-based system started in Canada in 1967, and the government has control over how many people it grants visas to every year.
Meanwhile, as a part of a package of policies aimed at establishing Shanghai as leading innovation economy, it is now easier for foreigners to gain permanent residency in the city.
In California, the focus was to secure flexibility on immigration policy for lower-skilled labour needs. Australia also has specific visa policies in areas with labour shortages, mainly in smaller, rural areas. The disadvantages of a points based system are that it doesn't leave employers in charge of the skills that come in.
As Alp Mehmet of anti-migration group Migration Watch UK put it: "A points-based system might suit the Australians who are trying to increase their population but, in fact, it is extremely complex and would be a non-starter for the UK."
How would it work?
Before London could have its own visa system, there would have to be a London-wide referendum on the question. But the referendum would need Parliament's approval, or it could be rejected by the government. A Tory government approving a Labour mayor's proposals? Unlikely.
Let's assume the referendum goes through. Whitehall would still play a role in scrutinising visa applications. The number of approvals would likely be based on London's skill shortages. While a London visa would not mean devolving decisions, the mayor and possibly businesses would be able to "sponsor" a certain number of visas, entitling holders to work in the city.
In her article, Hanna demonstrates that by taking a high-skills, points-based approach to the visa system, the likelihood of London visa workers leaving London for elsewhere in the UK is very low, given the fact that most of the country's highest-skilled jobs are in highly concentrated in the capital.
Is it likely to happen?
Migration Watch UK's Mehmet claims that just because the system works in Australia and Canada, doesn't necessarily mean that it would work in London, one of the main arguments being that they are much larger areas.
And let's not forget there's no love lost between the government and the Mayor of London. The government's reluctance to give TfL control over Southern rail, at Khan's request, is indicative of the stumbling blocks such a plan will face.
Nonetheless, Professor Tony Travers of the Department of Government at the LSE thinks otherwise. During the first meeting of the London Assembly EU Exit Working Group, Travers said Brexit Secretary David Davis supports Northern Ireland and the Republic of Ireland's open border. This means a country in the EU and one that isn't will have access to an "unpoliced open border, with a common travel area".
If that could be organised, he argues, then the government is capable of handling regional immigration policy for London.