Britain has repeatedly refused to countenance any extension to the talks into next year, saying if there is to be a trade deal, it needs to be done before Dec. 31. If there is no agreement, Prime Minister Boris Johnson has said Britain will "prosper" if it has to trade with the EU on WTO terms.

"The transition period ends on Dec. 31. As the UK has always made clear, this date will not be extended," said the official.

(Reporting by Elizabeth Piper, editing by Estelle Shirbon)