We must stay connected to the EU after Brexit – and London is the ideal bridge

London has always thrived by keeping in balance two quite different, and potentially opposing, visions of the city. First, is the idea of radical openness to the world: the cosmopolitan, global city. The second is that of a very local, very British city – insistently practical, rooted in British traditional needs and institutions – the national capital. London’s approach to Brexit needs to harness both dimensions.

Brexit must now get practical. For three years we have been trapped in the “whether” of Brexit. Careers were made on being for or against – not on trying to find pragmatic compromises in the middle ground. But the mayor’s job is fundamentally not about “whether” but “how”. And that means now making Brexit work for London.

The government’s position is clearer than it was three months ago. I was proud to be one of the 21 rebels who blocked a no-deal Brexit. No deal is now much less likely. But so too – sadly – are the softer forms of Brexit such as a Customs Union for which I campaigned, and over which I ultimately left the cabinet and the Conservative party. For better or worse, the government is more unified, its majority strong, and its red lines clearer.

London now needs to convince the government to pursue a Brexit based on three principles. First, London – and Britain – deserves to be safe. Security starts with intelligence, knowing where specific criminals are, what they have done and what they are planning to do; and using data to predict when and where an attack is likely to happen.

What is seen as local crime is often global: the man who commits a knife attack in Peckham might appear to be engaged in a local skirmish, but could, in fact, be the last link in a criminal chain that stretches back all the way to, say, the Hindu Kush​. Crime flourishes by exploiting the gaps between jurisdictions. Our membership of the European Union gave us rapid access to an unprecedented quantity of data on people and criminals, which made it much easier to track and match individuals, and to make arrests and extraditions work. This data access and security relationship should not be bargained away to secure other trading advantages. It is fundamental in its own right. And must be preserved.

The second principle is people. There are at least 900,000 EU citizens in the UK who have not yet sorted out their residency status. We must make that process easier, and there needs to be a presumption of forgiveness and generosity on the part of the Home Office when – inevitably – it turns out that people have got their paperwork wrong (or we will face a future Windrush). Taking back control was about sovereignty – it should not be about stopping the right people from coming to Britain. We can do much better with statistics and case studies to explain exactly how our care sector, our hospitals, construction sector, tech – and London business in general – depend on European immigration.

The third principle must be to preserve access to the European market. London leads the country in financial, legal, creative, audio-visual services, but we also have a surprising number of manufacturing and agri-food businesses. These businesses generally benefit from maximum access, which will mean minimum regulatory divergence. We need to ask patiently and clearly “what exactly is the advantage of this?” with every proposal on divergence.

There are some possible advantages (of looser solvency requirements on the insurance industry, for example, which could allow more investment in London’s infrastructure). But in general across most sectors, any advantage of divergence is outweighed by the disadvantage of losing market access. Governments need to listen to businesses. And to a London voice separate from business as well. Some businesses, for example, are prepared to relocate staff and capital to Europe, when ultimately London will suffer in losing that money, talent and taxes.

Once we have those foundations right, London should take the lead in doing what no politician here or in Europe has done – which is to define a good clear future relationship with the EU. London is the ideal bridge. Big cities are facing common issues – of which the environment is the most urgent and striking. We should tackle them by setting up an association of mayors of major European cities, to explore how we can learn from each other. Not just Amsterdam on bicycles but also Barcelona on data, or Helsinki on rough sleeping. And we can use this as a model for broader UK-EU relations.

I would fund a London Erasmus scheme for university exchanges with Europe to replace the existing scheme. I would invest mayoral funds in more UK border force staff, to make it quicker for European Union citizens to get through immigration queues at airports and the Eurostar. We must make Europeans feel welcome.

All of these policies need to be amplified, not just through the mayor but through all the network of businesses and civil society. And, above all, we need to understand that the threats of Brexit to London will not just be felt through specific regulations but also through the much less easy to quantify issue of confidence.

Confidence from residents, businesses, investors that issues rely on much more fundamental actions, which are within the gift of the mayor. Our streets must be safer, our housing must be more affordable, our infrastructure must be made fit for the 21st Century (from broadband to Crossrail 2 and the electrification of our vehicles). All this is vital if we are to continue to thrive as the greatest capital in Europe. And in this, as in everything, the key is not the principles but detail, rigour, grip and action.

Rory Stewart is a former MP and independent candidate for the London mayoral election