Hi Mike,
As I read the info on the PO website (second para below copied from PO site) an IDP MAY be required to drive in the EU only if there is a no deal Brexit. IDP's will still be required as usual for non EU countries but instead of these being available online as they were previously all IDP's will be issued by the PO.
Things are in a state of flux at the moment as the website says you need one for Portugal but the Portuguese have said that even if there is a no deal they will not require one.
Apparently all will become clear after the 29 March unless our worse than useless leaders kick the can into the long grass, in which case watch this space.
Post office info
"Information provided on the country checker tool is based on International Driving Permit (IDP) requirements for people travelling after 28th March 2019.
Please note that in the event of a ‘no deal’ Brexit, IDPs may be required for people intending to drive in EU countries after 28th March 2019, and this scenario is reflected in the information currently shown"
Dave