A partnership deal between New York and London was unveiled today as Mayor Michael Bloomberg met Boris Johnson on a lightning trip to Britain.

Mr Bloomberg, who was also feted by Conservative leader David Cameron on his visit, announced the cities would swap personnel and share ideas on tackling crime, improving transport, attracting business, keeping streets clean and boosting arts and tourism.

After an 80-minute meeting, Mr Bloomberg revealed that his main piece of advice for Mr Johnson had been to spend time building the best team of advisers and executives possible.

"Building a team is far and away the most important thing, even if it doesn't satisfy the press and the public may find it difficult to understand," he said.

Mr Bloomberg, the billionaire founder of the financial news service that carries his name, recalled that in his first days in office he was repeatedly asked what he was doing. "I said, 'I am working very hard in putting together the best team I can.' They kept coming back and saying, 'Yes, but what have you done? I kept saying, 'I'm building my team.'"

Mr Bloomberg, a Democrat turned Republican and now an independent, also told Mr Johnson to "be yourself" and try to implement his most unpopular policies early in his reign.

Mr Johnson's time as MP for Henley looks to be drawing to an end, after Mr Cameron insisted that there would soon be a by-election. "I think by-elections are like Shredded Wheat, it's best to have one at a time rather than three or four at a time.

"There will be a by-election and you won't have to wait too long."

Mr Cameron agreed there was much that London could learn from New York and dismissed suggestions that Mr Johnson had been "gagged" because he was not at the press conference.

Mr Johnson had a "packed schedule" the Tory leader stressed, meeting borough leaders and attending the opening of the new London Assembly.

"No one could ever gag Boris and it would be very unwise to try. We haven't hidden him away, I promise," he said.

Aides described talks as focusing on "practical, efficient, and effective policies" and advice on how to implement Tory campaign promises as swiftly as possible. Mr Bloomberg, who considered running for US president this year, was also expected to advise Mr Johnson on just how to unite the city's different political affiliations. In what is generally considered a Democrat city, Mr Bloomberg has twice been elected by putting himself above party politics.

Other areas of policy on the agenda included how to make City Hall more transparent and accountable and how to get better value for money for taxpayers.

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