Ivan Rogers came under fire for saying it could take 10 years for London to conclude deal with the bloc

UK's ambassador to the European Union resigned on Tuesday, adding uncertainty to the Brexit process less than three months before the country is due to trigger its departure negotiations.

Ivan Rogers, a highly-regarded diplomat who had been due to end his four-year stint in October, stepped down as London prepares to invoke Article 50, which starts a two-year countdown to the United Kingdom leaving the European Union.