I'm saying a pinky promise (to join the Euro, never to do so) would not be sufficient to reassure the British establishment or electorate of losing fiscal sover

I'm saying a pinky promise (to join the Euro, never to do so) would not be sufficient to reassure the British establishment or electorate of losing fiscal sovereignty. I don't understand why the EU would want this either. It would have to be an explicit "The UK has full fiscal sovereignty".