British Foreign Secretary Liz Truss unveiled on Monday plans to override some post-Brexit rules for Northern Ireland on the grounds that they create unacceptable barriers with the rest of the UK. But Prime Minister Boris Johnson’s government was warned about such problems after striking his very own 2019 Brexit deal, which it is now proposing to unilaterally change in a move that critics say undermines Northern Ireland’s economic stability – and analysts say is vulnerable to a Commons rebellion.