I wonder whether part of what is going on is more complex than that, and centres around enforcement and dispute resolution rather than substantive commitment. (The intended landing point being: we’ve voluntarily agreed these rules but “they won’t be enforced by the ECJ”.)
That is to say that the UK Government may well be prepared to apply EU rules in some areas (eg Tim’s example of Dublin III), but wants that enforced via the Joint Committee mechanism: ie where the UK appears to be departing from EU law, that is raised and arbitrated via the JC.
However, that approach will often mean that the ECJ becomes the binding arbiter: because any JC mechanism to which the EU signs up must always provide that the ECJ is the final arbiter on what EU law requires. So there is a bit of smoke and mirrors here.
See my thread yesterday evening.
