When UK Labour Regains Power, Should It Reverse Brexit?

[Cassius]

Aside from the above points, it'll probably be (at least) a decade before we could feasibly re-join, by which time the UK's import-export structure and regulatory system will likely have changed quite considerably due to the new relationship with the EU (as they did after joining the EEC in 1973). Opponents of re-joining could quite validly point to the disruption that re-entering the common market and the customs area after a long period outside could cause.

[Cassius]

When the UK was in the EU, it secured a huge range of opt-outs, while enjoying all the benefits of the single market, and actively resisted initiatives to further federalize the union.

It was a little more complicated than that: the Single Market was actually Mrs Thatcher's idea. And as that fact demonstrates, the big problem was always a fundamental lack of consistency.

I'm not sure that's strictly true, I think it's more the case that Mrs T's ideas changed, on the basis of experience (and Delors) once she got into her third term (and got closer to Powell's views on the relationship between the UK and the EU, albeit from quite a different direction).