The next round of talks begins on Monday and will be held face-to-face for the first time since the coronavirus epidemic spread in March.
But tempers have flared in recent days and Prime Minister Boris Johnson insisted on Saturday that Britain was quite ready to accept the consequences of no deal if common ground can not be found.
David Frost, Britain's chief negotiator with the European Union, will complete the Brexit talks even if he takes up his new position as national security adviser before they have finished, Johnson's spokesman said on Monday.
He added: 'UK sovereignty, over our laws, courts, or our fishing waters, is not up for discussion'.More news: Italy seizes 14 tons of amphetamines, said to be ISIS made
"I want to be clear that the Government will not agree to ideas like the one now circulating giving the European Union a new right to retaliate with tariffs if we chose to make laws suiting our interests". A transition period, during which Britain remains in the European single market and customs union, expires on December 31 and pressure is mounting to agree a free trade deal before then.
Without a new settlement, the two sides would see ties lessened to minimum criteria set by the Earth Trade Business with significant tariffs and severe disruptions to organization.
The latest round of Brexit trade talks gets underway in Brussels on Monday, with both sides hoping to break the deadlock that has stymied discussions so far. We need to make sure businesses can prepare properly for what will happen at the end of the year.
The talks are now more streamlined than early rounds that involved hundreds of negotiators.More news: How the world reacted to China’s national security law for Hong Kong
In a tweet, Frost reported he was coming to Brussels in "fantastic faith".
The discussions will start out with a assembly among the two men at 0800 GMT and will carry on throughout the week with shorter classes on the most problematic matters.
This could be either a very broad deal covering all areas of the relationship, as the Europeans want, or a simple trade agreement with small sectoral side deals as sought by London.
Regarding fishing issues, European Commissioner Virginijus Sinkevicius said: "We aim to reach an agreement that would allow for access to United Kingdom waters as of 2021".More news: 81 killed in Ethiopia unrest after activist shot dead