From Ducky McDuckface in the comments:
Naked exercise of the power. The EU, particularly the way the UK government chose to implement membership, means that ministers and civil servants have a great deal of latitude in the development and implementation of regulation and legislation before the concept of oversight from the Commons ever begins to intrude. If you are a member of an opposition party, this is the position you desire. Brexit raises the spectre of actually having to justify themselves and their actions to the Commons (and thus all the way down to us plebs) before they do it, and afterwards. This is utterly unthinkable, and must be avoided at all costs. As far I can see, the Ultra position is inexorably trending towards abandoning representative democracy in any useful form. There will most likely be attempts to bind the Commons internally via legislative proposals, and legal manoeuvres via the Supreme Court, and Miller established that this was effective. Since we're talking about a date at the end of March, this sort of thing could arise really quite quickly.