It seems Scotland and Northern Ireland must agree on invoking Article 50

Theresa May has indicated that Brexit could be delayed as she said she will not trigger the formal process for leaving the EU until there is an agreed “UK approach” backed by Scotland.

The Prime Minister on Friday travelled to Scotland to meet Nicola Sturgeon, the First Minister, and discuss plans for Britain’s Brexit negotiation.

In a sign that the new Prime Minister is committed to keeping the Union intact, she said she will not trigger Article 50 – the formal process for withdrawing from the EU – until all the devolved nations in the country agree.

That is from The Daily Telegraph.  Here is my previous post on whether Article 50 ever will be invoked.