We're dealing with film equipment carnets constantly around the world, and yes, they're a pain. Checking of the serial numbers down to individual batteries - can, and often does, take hours! Not just at each border, but the preparation/organisation in advance ensuring that the carnet information is correct (cross-checked with the gear that is going). That's before something is added (or also removed) just before departure!
The idea that this will carry across to UK European shoots is a horror I hadn't previously considered.
I'll add it to the list of unexpected/unintended consequences.