Boris Johnson signs BBC journalist Guto Harri as his chief spin doctor

The Welsh former journalist, a friend of the new London mayor's for 20 years, will start on Monday as director of communications.

His recruitment as a chief spokesman, revealed in the London Evening Standard, is a coup for Mr Johnson, who was today meeting New York mayor Michael Bloomberg.

The pair today announced a partnership deal between their two cities which aims to share the best policy ideas on everything from slashing crime to improving transport.

Ahead of the meeting Mr Johnson said: "Mayor Bloomberg has shown inspirational leadership and I am delighted we are establishing this new era of co-operation."

The London Mayor has known his new spin doctor, who is 41, since they met at the Oxford Union two decades ago and sealed the deal in a 90-minute chat in Mr Johnson's back garden last Sunday.

"I remember Boris Johnson as a sharp, witty, highly impressive figure even when we first met and I was 19 and he was 20," he said.

"I knew then that he was going to be a brilliant columnist, but he has now proved himself to be a serious political figure with a great vision that has captured the imagination of Londoners. It's a privilege to be asked to help him to put that vision into practice."

At the BBC, Mr Harri's reporting career spanned Westminster, New York and Rome covering politics and business.

He left the corporation two months ago to work for PR agency Fleishman-Hillard, spending four weeks as an adviser to Zimbabwean opposition leader Morgan Tsvangirai.

Mr Harri - who is married with twin sons aged six - went to primary school with Ffion Hague, the wife of shadow foreign secretary William Hague, and both belonged to the London-based club SWS - Social, Welsh and Sexy.

He was also approached to work for David Cameron last year.

As a journalist, Mr Harri interviewed Mr Johnson around a dozen times. "There is a reason why he is one of the best known politicians in the UK and why he has captured the imagination of people beyond the Conservative Party," he said.

The Mayor's own imagination seems to have been captured by Mayor Bloomberg whom he shared breakfast with at City Hall this morning.

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, a billionaire businessman who considered running for US president this year, was also expected to advise Mayor 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 the partisanship of normal party politics.

Areas of policy on the agenda included how to make City Hall more transparent and accountable, how to get better value for money for taxpayers and improve policing.

The Mayor was also today attending the opening session of the new London Assembly, as well as meeting the leaders of all the capital's boroughs along with race chiefs.