BRUSSELS (AP) — The European Union's Brexit negotiator said Wednesday that an agreement on Britain's exit "is within reach" if negotiations make progress ahead of a summit next week.

Michel Barnier said that up to 85 percent of the work on a deal is done but that the issue remains of how to ensure a transparent border on the island of Ireland.

He offered suggestions to make sure border checks are be kept to a minimum. Yet he also warned that some British proposals as they stood would give the U.K. too much of a competitive trade advantage.

With good will from both sides, he said, "agreement is within reach if we have the negotiations on the 17th of October," when Theresa May will meet her 27 counterparts in Brussels.

EU Commissioner Dimitris Avramopoulos told reporters Wednesday that Barnier and his team "are working day and night to reach a deal."

Britain is to leave the EU on March 29 and the possibility of there being no deal on future relations — particularly trade — is worrying businesses and politicians.

As part of the EU, Britain benefits from seamless trade with the bloc, its biggest trading partner. And the question is how to let Britain exit the EU without too much disruption to trade and without reinstalling a hard border between the Republic of Ireland and Britain's Northern Ireland.