But they missed their window after Brexit to strike the trade deals they needed, and now any trade deal they make will probably be under quite unfavorable terms.
Trade deals are multi-year projects and the terms you can get depends on how much leverage you have. Its noy the kind of thing you jump into after leaving a bigger trade bloc. The UK wasn't going to be able to negotiate anything without the bargaining chip of duty-free access to 500m customers.
That was always going to be the case. Brexit fantasists thought they were going to recreate the empire with UK at its center. They also thought they could do a deal with USA. What does UK offer USA if they're not in Europe?
It's unclear that there ever was such a window, given the _sort_ of Brexit they did. By far the most important trade goal for Britain would have been maintaining access to the European market on similar terms to previously (or at least similar terms to, say, Switzerland); everything else paled in comparison. But the form of Brexit chosen made that impossible.