What's Stopping You, Gordon?

Gordon Brown is of course quite right that any re-visitation of the devolution settlement automatically puts the whole of it back on the negotiating table. But there is a perfectly good answer to any hint of “taking powers back”. You can’t take back what you never gave away. Or, as Enoch Powell put it, “power devolved is power retained”. The Parliament of the United Kingdom reserves the right to legislate, overridingly, in any policy area it likes. Anyone who doesn’t like that should have opposed devolution, which they never, ever did. So, Gordon, what’s stopping you?