One wonders how they could negotiate anything better than then current zero tariffs they have with the rest of the EU? And why they think they would be in a better negotiating position than the entire EU for any other bilateral deals. @tomorton is right about the politically speaking results, but from an economically speaking perspective it's almost impossible to see a way they end up anything better than where they are now and most probably worse.
The thing is, they stop trading with the EU and start trading with the USA, just because there is 3000miles of sea rather than a 20mile tunnel between us is irrelevant to them, they actually think they'll get better back handers lets be honest, all about the deals and the back handers, none of this is for the uk public.
If this happened in the Russia, Putin would shoot everyone literally until they started working for the people, where as democracy, you vote for them, they screw you over, it's your fault you voted for the wrong assholes.