Boris Johnson was elected Mayor of London in May 2012 - this being the start of his second four-year term, taking him through to May 2016. At the time of his election he was repeatedly asked if he would stand for parliament while still being mayor. He always answered no to this question. He pledged that if elected he would be mayor and only mayor for the full term. Two years previously, in 2010, parliament had adopted a fixed five year term so Boris already knew the dates involved.
Last week Boris was adopted as prospective parliamentary candidate for the very safe Conservative seat of Uxbridge and South Ruislip. So safe that last time the Conservative candidate got more than twice as many votes as the next candidate (Labour).
The Tories of Uxbridge and South Ruislip are presumably content to be represented by a liar.
Boris has generally been quite successful at having his cake and eating it. Before he was mayor he was an MP, and before he was an MP he was a journalist. Before he was a journalist he was a management consultant, however he couldn't understand spreadsheets so he gave that up.
However he doesn't make a habit of giving up the previous job when he gets the next one. He remained a journalist after being elected MP for Henley, and remained for a while MP after being elected mayor. He took quite some persuading to give up parliament after being ensconced as mayor in County Hall. He has never given up being a journalist which still earns him about a quarter of a million pounds a year - this he describes as chickenfeed - although it is more than his mayor's salary.
Boris gets what he wants by bluster, waffle, bravado, and outright mendacity when the first three don't work. His superficial charm masks, albeit badly, a grasping, massively selfish personality. The more you learn about Boris the less you like him. He's not stupid but he lacks morals.
Boris probably anticipates a Conservative loss at the general election next year, followed by a Cameron resignation and a vacancy at the top. He will then seek to become Tory leader and thereafter Prime Minister in 2020.