Boris needs a hand with the computers on his first day in the job

(PA)

The first day in a new job is always stressful. But when you are in charge of a £11bn budget covering buses, the Tube, police and fire services for one of the greatest cities in the world, you can be forgiven for having a few first-day nerves.

Normally on a balmy Bank Holiday Monday, Boris Johnson might be expected to relax with his family in the back garden, wearing a pair of baggy shorts and grilling burgers on the barbeque – a chilled glass of Chablis in hand. But yesterday, in a neatly pressed navy suit, Mr Johnson arrived at London's City Hall, cappuccino and croissant in hand. Heading for the airy eighth floor office, the new Mayor of London had a simple message: he was going to roll up his sleeves and get down to business.

Gone was the dishevelled look that endeared him to voters. Instead, he managed to perfect the image of a keen young executive as he settled into the office vacated 24 hours earlier by Ken Livingstone. This was his more serious side – the "New Boris" that he proclaimed during the campaign – even if he could not help grinning like a boy with a new toy.

There was the odd glitch as photographers documented his first day at the office. One of the Mayor's aides had to show him how to log on to the computer system so he could write his first orders to the 750 staff that he will have working under him. But although he has a penchant for Greek and Latin, Mr Johnson is now expected to use plain English.

Mayor Johnson, who cashed in on his box office appeal to oust "Red Ken" after two terms, quickly got to work, attempting to disprove those who claimed he was merely a gaffe-prone joker. He announced the appointment of a former prison governor, Ray Lewis, as a new deputy mayor for young people. Mr Lewis, who is black, will help to reassure ethnic minorities about the Mayor's commitment to inner-city problems.

Michael Bloomberg, the Mayor of New York, is to fly in for a meeting on Friday, at which Mr Johnson can garner tips on running a big city. He will also have to build bridges with Tessa Jowell, the former Blairite cabinet minister who campaigned for Mr Livingstone and described Mr Johnson as a "joke" who would be a '"disaster" for London. She is also Gordon Brown's minister for the Olympics, so will have to work with the Mayor to deliver the 2012 Games for London.

The new Mayor's speech in praise of Mr Livingstone on election night may have been penned by Steve Hilton, David Cameron's strategy guru at Conservative Central Office. Mr Cameron is keen to ensure the Tory "brand" which he has restored is not spoilt by mistakes in City Hall. There is a widespread assumption that Mr Johnson will be put on a tight leash by Mr Cameron.

Ironically, Labour insiders say Mr Johnson could be helped to make a success of his new job by Gordon Brown. "Gordon increased Ken's powers and increased his budget. He gave Ken millions to spend and now that is all going to be for Boris," said a former Livingstone aide. "It's one of the ironies of life that if Boris is a success, he will owe it to Gordon Brown."