As someone that has (when forced and there was no alternative) moved stuff across frontiers professionally, that little paperwork can be a major pain in the arse.
See grizewald's opinions about what will happen with stuff sent to Sweden.
The clown has already started down that path. Today's papers report "The PM shrugged off 'hysteria' over issues like chlorinated chicken, joking that he thought Americans looked 'pretty well nourished'." He (and we) are about to find out how little bargaining power the UK has.
Yeah I guess if you have to do it as part of your job on a daily basis it's going to be a pain; for someone that might have to do it once a blue moon, it's less of an issue.
Arguably not.
If you look at customs declaration CN22 (that you put on the outside of something you send), you need to fill in the "HS tariff number", and sign that it is correct. If someone decides it is wrong, you have committed a criminal offence against a state. If that state is the UK, then you may find out just how powerful HMRC can be. Hint: they can do many intrusive things that the police cannot, e.g. bash your door in without any form of warrant.
Consider selling a nonfunctional Solartron 7081. Is that a DVM? (It doesn't work). Is it an antique? (It is certainly obsolete)
Consider selling a Julie Research VDR107 7 decade kelvin varley divider. There's no category for that, so what do you put? If you think of it a potentiometer, it might be 85 33 39, or 85 33 40 90, etc. Or using a different search path, it might be a 90 30 33 20 90, or 90303900 or 90308900. But the latter may provoke immune responses!
Remember the penalties for getting it wrong. The principals in the Matrix Churchill affair only narrowly escaped long prison sentences when a minister (Alan Clarke) admitted he had been "economical with the actualité". None of the current bunch would think twice about lying through their teeth!
So, more than a little pain for the occasional user.
P.S. the Matrix Churchill example isn't too far fetched. I once had to import an HP8770, which turned out to be classed as a
munition requiring heavyweight authorisation!