“Ever heard of the “Bohemian-Gay Index”? I know it sounds silly but it’s actually a serious measurement, created by the influential academic Richard Florida to help explain why some cities have higher levels of economic growth and innovation than others.

Florida’s insight is that urban areas that are attractive to creative people, and welcoming of diverse communities such as gay and bisexual people, tend to grow more quickly and create more jobs. In other words, places that score highly in the “Bohemian-Gay Index” are likely to prosper, and those that rank poorly typically lose out.

Florida argues that there’s a “global creative class” of educated people who are highly mobile and choose to move to cities they find attractive, starting businesses and sparking regeneration wherever they go. Places such as San Francisco and Seattle have done well on this front, for example, and it’s no surprise that these two cities have grown rapidly in recent years, as well as spawning world-leading companies such as Microsoft, Amazon, Uber and Airbnb.

The reason this index seems to be such a good predictor of a city’s prosperity is that the creative industries are a massive driver of economic growth today. According to the Greater London Authority, creative and tech companies employ more people than financial services and banking, and contribute £35 billion to the capital’s economy every year.

London has clearly done well in the past couple of decades when it comes to attracting the global creative class — our openness, diversity and cultural energy are all magnets for the brightest and best. However, as the Labour mayoral candidate Sadiq Khan points out, the latest statistics show more young people are moving out of London than at any time since records began.

What’s going wrong? The big issue is (obviously) the cost of housing, where the failure to reform the planning system and break the cartel of volume housebuilders has seen rents rise much faster than salaries. But we’ve also seen 40 per cent of London’s music venues close in recent years, in addition to poorly defined immigration rules that make it harder for talented creative people to come here.

Meanwhile, other cities are rapidly becoming more attractive to the global creative class. In the US, New York creatives and San Francisco tech entrepreneurs are moving in droves to Los Angeles, where it’s cheaper to live well, and in a city with a thriving art and music scene.

Here in Europe, Berlin continues to exert a pull but it’s Lisbon that’s really on the up. With abundant cheap space, great galleries and bars where you can stay out late without any hassle, Portugal’s capital has become the place to be. This year, for example, Europe’s largest technology conference, the Dublin Web Summit, is moving from Ireland to Lisbon. My company Second Home is following suit, and we’re launching a building in Lisbon in a few months — our first outside London.

London continues to be one of the most attractive places in the world for talented, creative people. But we can’t take that for granted — unless we take the right steps, places such as LA and Lisbon will do well at our expense. If the global creative class starts to move to other cities, it won’t just be our cultural life that gets poorer, it’ll be our economy too.”

By Rohan Silva for the Evening Standard