THE UK will “never” accept a so-called customs back-stop plan, which applied only to Northern Ireland and not the whole of the UK, Theresa May has insisted, as this would create an internal border and undermine the Union. . http://www.heraldscotland.com/news/16279867.No_10_makes_clear__UK_will___39_never__39__accept_customs_plan_for_just_N_Ireland/