Former New York mayor Mike Bloomberg had one major piece of advice for Boris Johnson

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Michael Bloomberg and Georgina Bloomberg attend the 'China: Through The Looking Glass' Costume Institute Benefit Gala at the Metropolitan Museum of Art on May 4, 2015 in New York City.

Mike Bloomberg, CEO of Bloomberg LP, is one of the few people out there qualified to give advice to a mayor of a major international city.

He ran New York for 11 years.

When he was in London on Thursday at a Goldman Sachs event to help small businesses, he had some advice for Boris Johnson on how to take London forward.

Boris needs to "include as many people as possible" in the city's success, Bloomberg said.

"He needs to make sure crime stays low, improve the school system, attract businesses and maintain London as a cultural centre," Bloomberg said.

Appearing on the stage with Goldman Sachs' investment-banking co-chief Richard Gnodde, Bloomberg said: "Johnson is doing some of those things but it's a big problem that he doesn't have control over the schools and the police."

With London property prices rising to unaffordable levels, Johnson's task of including lots of people, rich and poor in London's prosperity isn't going to be easy one.