Would I be stupid to take a gap year Economics

I've gotten offers from Nottingham, Leeds, Liverpool and Durham for economics, and applied to Warwick but I'm expecting a rejection due to low TMUA. I've realised I'd find a social+public policy/ development and economics course more interesting. I think I can achieve a*a*a in my a levels and there's some courses like economics and GSD at Warwick, ISPP with economics at LSE, development economics at Manchester that really interest me. I think I do want to do policy making as a career but I don't want to limit my options too much immediately. I'd need to reject my offers then reapply independently next year I think and I'm not very sure how that works either with having a reference etc. What should I do, would I be harming my career prospects by doing this?

Congratulations to your offers.
Taking a gap year is a big decision. First of all, I would suggest looking into the structures of your offered courses and your newly preferred courses to see the actual differences to ascertain whether you still want the change.
If you are determined to change course, you may see whether the courses are still open to application. You may decline all the present offers and apply to your newly preferred course and uni via Extra.
If you have decided and are determined, act quick.

I've gotten offers from Nottingham, Leeds, Liverpool and Durham for economics, and applied to Warwick but I'm expecting a rejection due to low TMUA. I've realised I'd find a social+public policy/ development and economics course more interesting. I think I can achieve a*a*a in my a levels and there's some courses like economics and GSD at Warwick, ISPP with economics at LSE, development economics at Manchester that really interest me. I think I do want to do policy making as a career but I don't want to limit my options too much immediately. I'd need to reject my offers then reapply independently next year I think and I'm not very sure how that works either with having a reference etc. What should I do, would I be harming my career prospects by doing this?

If the courses they want are available, and still open, at the Unis that they have already applied to, they don't need to wait for Extra - just email the Uni - and they could still defer any switch-offer they received and take a gap year.

Thankyou, I don't really want to do a politics and economics course as I'm not interested by political theory and stuff, and I still want atleast a component of economics in my course. Unfortunately except for Warwick none of the unis I've applied to offer a course like this, is it possible to email Warwick asking them to consider me for a different course?

Yes - definity worth a phone call - an email could mean weeks before you get a response - so do it quickly.