Interviewed for a new Channel 4 documentary, Woody Johnson questioned why the UK was so nervous about the prospects of leaving the EU, a process that in his view need not present a major challenge.
His comments come soon after Boris Johnson, the Foreign Secretary, told a group of Tory donors that if Donald Trump was in charge of Brexit actually you might get somewhere .
It came as Philip Hammond, the Chancellor, insisted the Treasury was not the enemy of Brexit but rather the champion of prosperity for the British people outside the EU.
Mr Hammond also accused Brussels of making a land grab for the City and harbouring an ambition to force the location of business into the EU.
On Thursday Sajid Javid, the Home Secretary, admitted that hardened criminals from EU countries could be given the right to live and work in the UK because EU rules prevent the Home Office carrying out blanket criminal records checks in foreign countries.
Brexiteers claimed the immigration deal for EU citizens living in Britain, unveiled by Mr Javid, was too generous as it emerged that almost 4 million people could apply for so-called settled status 600,000 more than previously thought. They will also be able to bring family members including boyfriends and girlfriends of more than two years standing.
Mr Johnson who took up his post last November said nervousness about Brexit had surprised him, adding that as an American Im just not used to hearing that.