I am not at all surprised at this ruling.
The long term trend of the UK courts, since they invented the doctrine of judicial review after WW2,
is to regard themselves as superior to the government and to overrule them whenever they can.
The way it usually works is that the lower courts take the view that the government has a job to do
and are generally supportive of the government using its discretion, the higher courts enjoy raising two
fingers at the government and the supreme court then decides that it may not be the best idea to obstruct
the government if what the government is trying to do makes sense and does not involve any injustice.
I don't think it is much to do with UK parliamentary sovereignty.
However it is quite hilarious how many Remainers who were only too happy for UK sovereignty
to be eroded in the transition to an ever closer union, are suddenly insisting that sovereignty resides
in the UK parliament rather than in the will of the UK people as a whole as expressed in the referendum.
This will no doubt go to the UK supreme court.
However I am waiting for the European Court to jump in and say that as there is no prexisting constitutional
requirement (see line 1, below) in the unwritten UK constitution, there is no right for the UK to leave at all.
I.e. that Article 50 is meaningless window dressing, which if it occurs will indeed cause real trouble.
Article 50
1. Any Member State may decide to withdraw from the Union in accordance with its own constitutional requirements.
2. A Member State which decides to withdraw shall notify the European Council of its intention. In the light of the guidelines provided by the European Council, the Union shall negotiate and conclude an agreement with that State, setting out the arrangements for its withdrawal, taking account of the framework for its future relationship with the Union. That agreement shall be negotiated in accordance with Article 218(3) of the Treaty on the Functioning of the European Union. It shall be concluded on behalf of the Union by the Council, acting by a qualified majority, after obtaining the consent of the European Parliament.
3. The Treaties shall cease to apply to the State in question from the date of entry into force of the withdrawal agreement or, failing that, two years after the notification referred to in paragraph 2, unless the European Council, in agreement with the Member State concerned, unanimously decides to extend this period.
4. For the purposes of paragraphs 2 and 3, the member of the European Council or of the Council representing the withdrawing Member State shall not participate in the discussions of the European Council or Council or in decisions concerning it.
A qualified majority shall be defined in accordance with Article 238(3)(b) of the Treaty on the Functioning of the European Union.
5. If a State which has withdrawn from the Union asks to rejoin, its request shall be subject to the procedure referred to in Article 49.