Does Michael Bloomberg know how dangerous a Labour government would be?

In our lifetimes, alas, we have seen how it temporarily lost that crown. For much of the post-war period, few would have been so foolish as to rate London above New York. We lagged behind in dynamism, in entrepreneurial spirit, in sheer energy – not to mention GDP.

Today, however – well: it is clear that in many key respects it is London that now has the lead.

It is not just that the British capital still has the largest financial sector on earth, with probably about 320,000 people involved in one way or another. I read somewhere that there are more American banks established in London than there are in New York itself, and London does far more currency dealing. Britain’s capital now has a bigger tech sector, with about 528,000 people employed in all manner of start-up industries, and a creative sector expanding so fast that in the next 10 years we will probably make more TV and feature films than either New York or indeed Hollywood.

We have more museums and galleries than New York; we have more live music venues. We have more world-class universities in London than there are in New York – four of the world’s top 10. We have more World Heritage sites, twice as many bookshops, far more bars and pubs, and a much lower crime rate (the murder rate in London was last year the lowest since the Sixties, and less than a third of the rate in New York), not to speak of wonderful taxi drivers who are obliged by law – unlike those in New York – to know where they are going; and a Tube network that is running ever faster and more efficiently; and if you add all these factors together you can see why people are so keen to come to our city.

David Cameron with Bloomberg in 2010

Last year London hosted 18.6 million visitors from overseas, beating the record achieved in 2013. It is now the world’s number one destination for international tourists – and all the cash they bring – knocking Paris and New York off the pedestal. That is to the best of my knowledge the first time in recent history that London has come first in this fundamental criterion of global popularity.

So let me say to Mike: you have done the apprenticeship, and done it with great distinction. Now is the time to step up to the plate, and take on the fastest-growing and most dynamic urban economy in Europe.

You will, of course, find many friends here – and, indeed, with your work at the Serpentine Gallery and on other projects you already contribute hugely to London life, and you know how much we have in common. Both New York and London are cities that boast their diversity, with about 300 languages spoken in each. We constantly imitate and learn from one another, in a spirit of friendly rivalry. We have both put in bike-hire schemes (ours, I think, a couple of years ahead of yours); we both pursue strategies of urban greening; we are both battling to improve air quality. We are both struggling to cope with the problems of success – above all, to satisfy the demands of all who want to live and work here by building enough affordable housing.

Another American politician admires one of London's bikes for hire

Each city has an amazing future – according to all reputable analyses – as a powerhouse of wealth creation and innovation. But before you start your campaign, dear Mike, there is one cloud on the horizon, one way that London could go backwards to the Seventies, and that is if the people of this country are so mad as to elect Ed Miliband next month. Labour’s policies would damage our universities, by depriving them of vital revenue for investment in teaching. Labour would hit financial services and jeopardise the jobs of thousands who are by no means affluent; and above all a Labour government would pursue policies of taxation and regulation that are diametrically opposed to the spirit of enterprise that enable you to build your own empire.

It would be a great thing to enter the glass spheroid in Southwark and become Mayor of London, Mike. But first we need to ensure a sensible Conservative government on May 7.

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