British negotiator David Frost confirmed Sunday that his country will not change its position during its talks aimed at reaching a post-Brexit agreement with the European Union.

"We are working to reach an agreement, but the only possible agreement is the one that is compatible with our sovereignty and that restores our control over our laws, our trade and our water," he said on Twitter upon his arrival in Brussels, where the last round of talks was starting. 

"This was our consistent position from the beginning and we will not change it."

Frost said he and his European counterpart, Michel Barnier, would resume direct negotiations Sunday.

The talks expected in the next few days are crucial to reaching any agreement before the time runs out at the end of the year when the post-Brexit transitional period expires.

Frost warned, "We may not succeed," noting that there is some progress, but stressing at the same time "important elements" that must be resolved.