Britain wants the European Union to show the same respect for legal autonomy it afforded countries such as Canada and Japan when signing trade deals with them, Prime Minister Boris Johnson's office said on Tuesday.

Johnson's office said Britain was determined to protect its legal autonomy in talks with the EU to agree a future relationship, which are due to begin next week. The EU agreed its negotiating mandate on Tuesday.

"The EU has respected the autonomy of other major economies around the world such as Canada and Japan when signing trade deals with them. We just want the same," Johnson's Downing Street office said on Twitter.

"We agree the UK's trade with the EU is significant. The U.S.'s is on the same scale — yet that did not stop the EU being willing to offer the U.S. zero tariffs without the kind of level playing field commitments or the legal oversight they have put in today's mandate."