Boris Johnson said on Wednesday the United States would be "in the front of the queue" following his surprise appointment as Britain's new foreign minister.
The Europe 1 radio interviewer told Mr Ayrault: "I've got the impression you're scared of being faced with the fanciful Boris Johnson", to which the French foreign minister replied: "No, I've got no worries at all about Boris Johnson". Johnson also drew accusations of racism during the campaign by suggesting in a newspaper article that U.S. President Barack Obama, whom he described as "part-Kenyan", was biased against Britain because of an "ancestral dislike of the British empire".
Mr Ayrault added: "His back is against the wall to stand up for the interest of his country but also to make the relationship with Europe clear".
"Great Britain has a new foreign minister".
Conservative lawmaker David Davis took the newly formed job of minister in charge of negotiations with the European Union that will set up the conditions for leaving.
The new PM wants more women in the Cabinet and a string of ministers will be hoping for promotion, including Andrea Leadsom, who dropped out of the Tory leadership race on Monday, handing Mrs May the keys to No 10.
Labour MP David Lammy summed up the reaction to Mr Johnson's appointment in a tweet, in which he wrote: "Boris Johnson as our Foreign Secretary?".
But Mr Whittaker said he did not believe Mr Johnson would have difficulties dealing with his German counterpart, pointing to his "international experience" promoting London around the world as mayor.
EU leaders including European Council President Donald Tusk condemned Johnson's comparison during the campaign of the EU's goals with those of Hitler and Napoleon. After that came to pass, he was seen as the favorite 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. Pic: Lauren Hurley/PA Wire File photo dated 29/02/16 of Boris Johnson (centre) swinging from a bus as Northern Ireland Secretary Theresa Villiers (left), Northern First Minister and DUP leader Arlene Foster and Minister of Enterprise, Trade and Investment Jonathan Bell (second right) look on during a visit to Wrightbus Chassis plant in Antrim. Her appointment reflects a desire by Theresa May to maintain some balance between "Remain" and "Leave" supporters who were so bitterly opposed to each other during the referendum campaign.
Nevertheless, the normally soft-spoken former French prime minister Ayrault had a strong warning for the new foreign policy chief of his near neighbour. "We need now to send a shot of adrenaline through our diplomatic system so we raise our game all round the world".
"At this incredibly important time that will determine Britain's economic and cultural relations with Europe, it is extraordinary that the new prime minister has chosen someone whose career is built on making jokes", Farron said. His criticism of her government could have been particularly strong. Mr Johnson was "properly, properly hated", said Anne Gellink, the Brussels correspondent of public broadcaster ZDF. Those talks are expected to take as long as two years.
It wasn't the first time the former London mayor said he would give up his US passport.
A lot of Johnson's most controversial comments have been made in his column for the Daily Telegraph, the UK's leading right-wing broadsheet.
Johnson's quick reassurance also contradicts Theresa May who recently said that the future of European Union nations in the United Kingdom was still uncertain.