EU members cannot do that.
Funny! Do you know why so many countries stand in a queue to become member of the EU?
BECAUSE SO THEY DON'T HAVE TO NEGOTIATE ALL ALONE.
Because, just in case you don't know it, being part of a powerful economical union is a huge PLUS and makes even the most tiny country powerful and influential as the most big player in the bloc.
I'm not sure who or what told you the line that having to negotiate trade all by yourself, with only your tiny market and a few millions customers makes you in some way stronger or more successful as being part of a huge trading bloc of many millions square kilometer and paying customers.
Outside of being a huge country yourself...like...say...the US...or China...or even Russia that is.
Bratwurst Boy,you Germans underestimate us Brits...and your arrogance has cost you dear more than once.
Which arrogance do you mean?
The arrogance of"We are stronger together"?
or"Pffft...we don't need anybody. We are better off alone. They are only dragging us back anyhow!"
That outcome of Brexit is already defined not by arrogance but by economical logic...