Britain can still reach an agreement with the European Union in September, its chief negotiator David Frost said on Thursday even after the latest round of talks on a future relationship ended with "substantial areas of disagreement".

Since Britain left the bloc in January, talks on a trade agreement and other ties have all but stalled, with each side accusing the other of failing to compromise before a transition period runs out at the end of this year.

Britain is keen to strike out alone after Brexit, pursuing trade deals with other countries and setting its own sanctions regime, and again Frost said the EU's proposals failed to meet the government's demand to be treated as an independent country.

Frost said the chance of reaching an "early understanding on the principles underlying any agreement" would not be reached in July, with the two sides unable to breach the gap over fair competition and fisheries.

"Considerable gaps remain in the most difficult areas. That is, the so-called level playing field and on fisheries," Frost said in a statement.

But he added: "Despite all the difficulties, on the basis of the work we have done in July, my assessment is that agreement can still be reached in September, and that we should continue to negotiate with this aim in mind."