Britain's Brexit negotiator goes to work on an egg as first round of talks takes place in Brussels

"As we're going to have to budge with the US, I can't see it holding with the EU either," said Sam Lowe, trade expert at the Centre for European Reform.

The mandate for the US trade deal included not putting the NHS on the negotiating table and apparent pledges to prevent US imports of chlorine-washed chicken and hormone-injected beef.

"While the UK has dug its heels firmly in on any issues to do with the NHS, it has left itself some wriggle room on food, in that it commits to maintaining high, stringent standards but not necessarily the ones that exist today," said Mr Lowe.