The head of the World Trade Organization (WTO) said Sunday it would not be "the end of the world" if Britain failed to reach a post-Brexit trade deal with the EU, but there would be costs.

Roberto Azevedo told the Sunday Telegraph newspaper that although Britain would be better off with an agreement, the impact of falling back on WTO rules would be "manageable".

"About half of the UK's trade is already on WTO terms -- with the US, China and several large emerging nations where the EU doesn't have trade agreements," he said.

"So it's not the end of the world if the UK trades under WTO rules with the EU."

Britain intends to leave the EU's single market and customs union when it withdraws from the bloc in March 2019, but hopes to reach a free trade agreement (FTA) with Brussels before then.