On the modern property market Samuel Johnson might have said “When a man is tired of London, he is tired of its price.” With Londoners leaving to buy elsewhere, is this the dark side of an Alpha city status?

It’s a phrase so often quoted it’s almost become tired itself, but whether it’s a perfect London day (or a truly terrible one) I find myself thinking of Samuel Johnson’s words. “Why, Sir, you find no man, at all intellectual, who is willing to leave London,” said the writer, poet, editor, essayist and moralist. “No, Sir, when a man is tired of London, he is tired of life; for there is in London all that life can afford.”

Aside from the lack of gender neutral pronouns, these few lines from the 18th century still feel achingly relevant today, with one addendum.

London still has all that life can afford, but fewer and fewer people can afford that life. People in full retention of their intellectual faculties are leaving London in droves. In fact, it’s now being presented as the smart thing to do.

Glossy pictures in the weekend supplements show happy 20-somethings splashing in the sea and young couples clutching children who look a little bewildered to be breathing air not choked by fumes. Who knew one could achieve such quality of life beyond the confines of the M25? And you know your money goes so much further there.

Over 25 per cent of 25 to 35 year old Londoners surveyed plan to buy their first home outside of the capital, according to Online Mortgage Advisor. Of these 8 per cent had grown tired of London and cited a better quality of life as the reason to buy elsewhere. 27 per cent said was simply too expensive.

And it’s not just skint hipsters looking for cheap spaces to create their artisanal vinyl coffee cup business any more. It’s those already on the ladder who are moving out, only able to clasp the next rung if it’s fifty miles from they place where they grew up.

Bristol is already so full of Hackney exiles that the property market is well on the way to almost London levels. Margate and Hove are the latest destinations to worry about everyone savvier than you decamping to.

There are fears we’ve reached a tipping point. Savills have calculated there was a net migration of 93,000 people out of London last June, up 80 per cent from five years ago.

Those in their twenties are still tumbling in, searching for the kind of careers you still can’t forge elsewhere. Everyone else is scampering away to cheaper pastures new.

Londoners are victims of London’s success. All that life can afford means theatres stuffed the rafters with the latest shows and hottest stars, and art galleries dripping in gilt-edged masters, and an entire crèche’s worth of enfant terribles.

Hundreds of restaurants open every year, each with a new twist on a cuisine neatly filleted from a culture half the way across the world, and bars offer increasingly novel ways to knock back gin.

All these crunched up together in one relatively compact urban centre is what gives London its Alpha city status, combined with its (relative) political stability and a benevolant tax structure.

Sure you could take your millions to Geneva, but once you’ve sampled every flavour of Milka there’s little else to do. It’s our culture that brings all the wealthy buyers to the yard and has sent property prices inflating faster than wages could ever keep pace with.

Hampstead is London in microcosm. We have a brilliant arts scene on our doorstep and high streets full of real restaurants that keep the chains at bay. We have the wide expanse of the Heath for windswept winter walks and the cool depths of the ponds for summer dips. All a good life can afford, but it’s increasingly unaffordable.

But you can’t close the gates. You could sooner hold back the tides than the super rich, with a platinum and diamond encrusted version of the Thames Barrier.

People still pour into this grimy, glorious hub every day. London needs an international mix. It’s so globalised now that pulling the plug of overseas investment would be a shock it couldn’t withstand. That people from all over the world make their homes here is part of what makes the city so unique, diverse and special.

People will always have the energy and drive to live here, but when it’s exhaustingly expensive we risk losing the people that bring it to life.