“Just as a national driving licence issued in Laos does not permit the bearer to drive legally in the UK; a UK driver's licence has no meaning in Germany, except insofar as the EU has a common agreement that licences issued in one member state apply to all other member states.”
Quite so. But the likely situation post-Brexit is not so straightforward as you suggest as there is no common requirement across Europe for International Driving Permits to be held. Travellers from the USA, for example, need an IDP if they want to drive in Austria, Greece, Germany, Hungary, Poland, Italy, Slovenia, and Spain. They do not need one to drive elsewhere in the EU.
If common sense prevails (not a given by any means when the European Project is in any way jeopardised) it would seem most prudent to maintain the status quo between the UK and the EU on this matter. Yes, before Brexit this (and a multitude of other matters) will need to be clarified. That’s what we pay civil servants for. But talk of a “cliff edge” is ludicrous. Both sides will have had upwards 33 months to prepare by Brexit day. But instead of concentrating on things that matter (such as passports, driving licences and customs arrangements) they spent more than six months arguing the toss over how much cash we would be charged for the privilege of leaving.
To be pragmatic, what do you think will happen on both sides of the Channel on 30-3-19 if no agreement is reached and suddenly IDPs are seen as a requirement for EU drivers to drive in the UK and vice versa? Do you see border staff in both locations checking drivers’ licences and turning them round if they do not have the correct documents? People need to get real. Your lawyer friend is obviously well versed with the legal niceties of Brexit. But he doesn’t seem to have much to say about reality. The UK and the EU need to crack on and plan for a “no deal” situation. They need to tell people what driving licences they will need, what the validity on their passport is required and a wealth of other things. Simply throwing one’s hands into the air and wailing that it is all too difficult is not an option because believe it or not life will go on (on both sides of the Channel) after Brexit. The UK’s membership of the EU is a mutually beneficial arrangement (just) and now that it is ending both sides need to sort out the practicalities instead of trying to scare the populace witless. That’s been tried once and it didn’t work.