The main thing we'd lose is the autonomy to manage our own economy. Given that's something we've handled especially well resulting in impressive economic stability in spite of global events, it's not a thing to be sacrificed lightly - or at all.

The main benefit of joining the Eurozone is tight economic integration that lets member nations share the larger group's economic stability. That benefit is never going to substantively materialize for a nation physically separated by an ocean. But we'd still be losing the right to decide how many power coupons we print, directly regulate our own banks, and set interest rates/inflation targets.

I'm open to other forms of EU association, but the Eurozone is a solid hell no.