The European Union’s chief negotiator Michel Barnier on Monday appeared to welcome the idea of a customs union arrangement with Britain.

In a letter to May, UK opposition Labour leader Jeremy Corbyn suggested a “permanent and comprehensive UK-wide customs union” with the EU.

Corbyn’s suggestion appears to envisage Britain being part of a separate customs union, rather than part of the EU Customs Union (EUCU) itself. How this would be established or agreed upon in a matter of weeks is not clear.

The Labour leader envisages common external tariffs on goods from the rest of the world.

It also aims for Britain to have a say in future trade deals made by the EU.

While Barnier did not engage with Corbyn’s plan in detail on Monday, he said the idea was “interesting in tone and substance.”

“Something has to move on the British side,” Barnier told reporters in Luxembourg, where he had been meeting Prime Minister Xavier Bettel.