Boris Johnson, Britain’s most colourful politician with a long record of gaffes and scandals, has been appointed as foreign secretary in a surprise move by new Prime Minister Theresa May that could shake up world diplomacy.

The former London mayor, who has never previously held a cabinet post and is known for his undiplomatic language, was the most prominent figure in the campaign for Britain to leave the European Union that culminated in a vote for Brexit on June 23.

The appointment of a man who in the run-up to the referendum compared the goals of the EU with those of Adolf Hitler and Napoleon is likely to cause consternation in European capitals.

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Johnson also drew accusations of racism during the campaign by suggesting in a newspaper article that US President Barack Obama, whom he described as “part-Kenyan”, was biased against Britain because of an “ancestral dislike of the British empire”.

The US State Department was quick to say it looked forward to working with Johnson.

The rise to one of the four great offices of state was the latest twist in an eventful career for the man invariably referred to simply as “Boris”, known in Britain and beyond for his clownish persona and dishevelled mop of platinum hair.

Boris once took a friendly game of rugby with children way too seriously.

Johnson originally made his name as an EU-bashing journalist in Brussels, then entered politics in the Conservative Party while also raising his profile through a series of appearances on a hit comedy TV show.

His ability to charm people with his quick wit and eccentric style helped him shrug off a series of scandals.

Where others would have floundered, Johnson became increasingly popular, culminating in his two victories in usually left-leaning London’s mayoral contests in 2008 and 2012.

His decision to defy then-prime minister David Cameron by leading the push for Brexit was widely seen as a bold gamble to replace Cameron should the “Leave” side win the referendum.

After that came to pass, he was seen as the favourite for the top job, but in his hour of triumph his ambition was thwarted in dramatic fashion when his close ally Michael Gove abruptly deserted him and announced his own candidacy.

His appointment as foreign secretary was unexpected. In her previous role as interior minister, May had humiliated Johnson by refusing to allow the use of water cannons in England after, as mayor of London, he had bought three of the devices second-hand from Germany.

In a speech launching her own leadership bid on June 30, May made fun of Johnson by contrasting her own experience of negotiating with European counterparts with his.

“Last time he did a deal with the Germans he came back with three nearly-new water cannon,” she said to laughter.

With May having also appointed David Davis to the newly created post of secretary of state for exiting the European Union, Johnson’s role in detailed negotiations over the terms of Brexit is likely to be limited.

However, he will have to handle some of the most complex and explosive diplomatic crises around the world, from Syria to Ukraine.

“At this incredibly important time … it is extraordinary that the new prime minister has chosen someone whose career is built on making jokes,” said Tim Farron, leader of the opposition Liberal Democrats.

-AAP