European Union's chief Brexit negotiator Michel Barnier takes part in the EU Commission's weekly college meeting in Brussels, Belgium, March 6, 2019. REUTERS/Yves Herman

LONDON (Reuters) - Britain was “not impressed” by proposals from the European Union’s chief Brexit negotiator Michel Barnier saying the bloc was ready to give Britain the unilateral right to leave the customs union, a British government source said on Friday.

Barnier added in a series of tweets that Britain would still need to honor its commitment to preserve a border free of controls between EU member Ireland and the British province of Northern Ireland - something that in previous negotiations led to proposals to place a customs border “in the Irish Sea” between the island of Britain and its province.