Britain's main opposition Labour party will vote for Prime Minister Boris Johnson's post-Brexit trade deal with the European Union, its leader Keir Starmer said on Thursday.

"I can say today that when this deal comes before parliament. Labour will accept it, and vote for it," he said, adding it was in the national interest to do so given the alternative of no-deal.

But he criticised the accord as "not the deal that the government promised", calling it "thin" and voicing fears about the government's preparations for leaving the EU single market.