EU leaders endorsed stiff divorce terms for Britain on Saturday and warned Britons to have "no illusions" about swiftly securing a new relationship to keep their access to EU markets, Reuters reported.
"What this shows, and what some of the other comments we've seen coming from European leaders shows, is that there are going to times when these negotiations are going to be tough," May told the BBC.
May also reaffirmed her position that she would be prepared to walk away from the talks on leaving the EU without a deal if she did not like what was on offer from Brussels.