BRUSSELS, Dec 22 (Reuters) - The European Union’s Brexit negotiator, Michel Barnier, will update the bloc’s 27 national envoys on the latest on Brexit at 1500 GMT on Tuesday, with disagreements over fishing rights the key obstacle to a new trade deal, Brussels sources said. EU officials said Barnier would then also speak to the European Parliament’s Brexit group, adding that cutting the value of the bloc’s catch in UK waters by 35% from 2021 would be too high. (Reporting by Gabriela Baczynska; Editing by Alison Williams)