Despite the political impasse over how to extricate the United Kingdom from the European Union, the bloc's name is already being removed from its passports.
There were "no red lines" in the ongoing discussions, he told reporters, adding: "I expect we will reach some form of agreement".
A new and old passport.
Susan Hindle Barone, who picked up her new passport on Friday, said on Twitter she was "truly appalled".
May said earlier this week she would seek a delay that is "as short as possible" to the current Brexit date of April 12.
Britain was supposed to leave the European Union on March 29, but requested a delay after parliament failed to approve a divorce deal the British government had negotiated with Brussels to minimise disruptions.
At this stage the other 27 European Union members, which must give unanimous backing, appear unlikely to grant the extension.
Past year it emerged that Franco-Dutch company Gemalto had won the contract to make the new blue passports, prompting fury from Brexit campaigners and more ridicule from Remainers that a British company was not chosen.
A Home Office spokeswoman told the British broadcaster that delivery centers will continue printing the pre-Brexit EU-UK design until stocks run out "in order... to achieve best value to the taxpayer".
Both passports remain equally valid for travel, the Home Office said, and a new blue passport design would be rolled out from late 2019.
British passports had already become ensnared in the country's Brexit divisions after the government announced in 2017 it would return to traditional blue passports "to restore national identity". Once Britain has left the European Union, the old passports will no longer be issued.
"Burgundy passports that no longer include the words "European Union" on the front cover will be introduced from 30 March 2019", it said.