Well, one's said "major" and another has said "sizeable", so I'd be interested in how they're defined. But I'll happily bow to those who have done what they call sizeable.
I fail to see how any Brexit-related work stream could be protected from the political environment.
Let's face it, most change management begins with a change that someone has already decided ought to happen, and they won't take kindly to any consultation that fails to agree that it's worth doing, and most end with a change that fails to deliver the expected outcome. Congratulations if your sizeable programmes have been different.