LONDON (Reuters) – The European Union will not give a new mandate to renegotiate post-Brexit trade rules for Northern Ireland agreed as part of the Brexit deal, the bloc’s ambassador to London said on Thursday. Britain is lining up a new law that would effectively override parts of a Brexit deal and has said that the bloc’s refusal to budge on its negotiating mandate for the talks is “hugely disappointing”. Speaking at an event in Westminster, the EU ambassador, João Vale de Almeida, said that the EU would stick to its existing mandate for the talks with Britain. “We were told that we should g…