David Frost told the Mail on Sunday newspaper that Britain wants to get back the powers to control our borders and that is the most important thing.
Frost and EU negotiator Michel Barnier are due to meet in London on Tuesday for the eighth round of negotiations since Britain left the now 27-nation bloc on January 31.
That political departure will be followed by an economic break when an 11-month transition period ends on December 31 and Britain leaves the EU's single market and customs union.
The two sides are trying to strike a new deal on trade, security and a host of other issues, but talks are deadlocked.
The key sticking points are European boats' access to UK fishing waters and state aid to industries. The EU is determined to ensure a level playing field for competition so British firms can't undercut the bloc's environmental or workplace standards or pump public money into UK industries.
Britain accuses the bloc of making demands that it has not imposed on other countries it has free trade deals with, such as Canada.
Frost said Britain was not going to compromise on the fundamentals of having control over our own laws.
We are not going to accept level playing field provisions that lock us in to the way the EU do things, he said.
Both sides have downplayed the chances of a deal, though some of that rhetoric is muscle-flexing before crucial weeks of talks.
Barnier said last week he was worried and disappointed by the lack of progress and said the UK had not engaged constructively.
If there is not a deal, tariffs and other obstacles to trade will be imposed from January 1.
British freight firms warned last week there could be logjams at ports and supplies of key goods in Britain could be severely disrupted if there was no trade deal.