Brussels - The EU is ready to offer Britain the "most ambitious" free trade deal but its adherence to the bloc's rules after Brexit will be "decisive", the bloc's chief negotiator Michel Barnier said Monday.

Barnier held out the promise of a comprehensive free trade agreement (FTA) after Britain leaves the bloc in March 2019 if it settles divorce issues including its exit bill and the Irish border.

"If we manage to negotiate an orderly withdrawal and establish a level playing field, there is every reason for our future partnership to be ambitious. This is our preferred option," Barnier said in a speech in Brussels.

"This is why we have started internal preparations with member states to talk about the future as soon as we have agreed on how to settle the past," he told an event hosted the Centre for European Reform think tank.

"The EU will be ready to offer its most ambitious free trade agreement approach."

But Barnier warned that Britain had to decide whether to stick to EU standards on health, environment and workers' rights or align itself more closely with other parties, following a recent call by the US commerce chief for Britain to follow American rules if it wanted a US trade deal.

Watch EU negotiator Michel Barnier offer UK the prospect of a 'most ambitious' trade pact

"Does it want to stay close to the European model or does it want to gradually move away from it. The UK's reply to these questions will be very important, and even decisive," he said.

The answer would affect the ratification of any Brexit deal in national parliaments and the European Parliament, he said.

"I don't say that to create problems, I say that to avoid problems," added Barnier, a former French minister and European commissioner.

[h5p id="7"]