Brexit against the wishes of Scotland and Northern Ireland would violate the UK’s constitutional settlement

Scotland’s First Minister, Nicola Sturgeon, has indicated that she intends to explore options to protect Scottish membership of the European Union following the UK’s referendum on 23 June. But is it really possible for one of the constituent nations of the UK to block Brexit? Jo Murkens writes that if either Scotland or Northern Ireland rejects leaving the European Union, the UK as a whole cannot proceed with Brexit negotiations in any constitutionally plausible way. [Update 02/07/2016: read a continuation of this discussion here.]