Myself and a friend have both been stopped for a document check and each time both myself and my friend where told that we have to change our UK Driving Licence for a Portuguese licence.
Now my friend and I have both changed our driving licence as required by the GNR who found the page in the very thick book they carry in there car.
I now have no reason to worry at the end of the day i won't argue with the GNR. I doesn't matter what others have to say i would rather listen to the GNR than risk a fine.
Had you previously registered your UK licence with the IMTT and received a document proving it from them when you were told this? Because that is the alternative procedure and any traffic cop on the road should know that and accept your UK licence plus the document. I'd be very surprised indeed if it's any different where you are, which, compared to here is positively thronging with tourists and foreign residents. They will also be coming across any number of Portuguese citizens who've lived and worked abroad and returned to Portugal bearing foreign driving licences. I'm sure they know the rules inside out.
The rules, incidentally, state that you must register or exchange within 60 days of becoming resident in PT, so if you were outside that period when you were apparently told this, that was risking a fine and the GNR were very kind to you indeed.
Similarly the old paper licences were valid until the holder reaches 70, once someone becomes resident in PT the PT rules on renewal ages become active (60, 65, 70). The same also applies to UK photocard licences that have a 10 year validity. E.G someone aged 56 renews their UK photocard licence before leaving the UK to take up residence in PT, they would think that their licence is OK until it expires when they are 66 whereas to the strict interpretation of PT law their licence ceases to be valid when they are 60.
A licence from another EU state, registered in PT, is valid until whatever date or age applies under that state's laws, regardless of the PT age thresholds. It's not required to be re-validated or exchanged until whatever date is printed on the licence (or, presumably any age that has been subsequently applied in that home state), at which time it then has to be exchanged or re-validated to comply with PT rules.
BUT whilst I'm more than happy to argue with a UK cop when they're wrong, had I been told by the PT cops that stopped me that I had to exchange my licence I would have done so simply to avoid the aggravation knowing that at some time I'd have to change it anyway. And to be honest I can't actually think of any reason why I didn't swap to a PT licence as soon as I moved out here, it was just laziness on my part and that isn't a valid reason.
I wouldn't see any reason, if it arose with me, not to question it politely and to point out that the information is available on the IMT's website and links from it. But it's never arisen although I've been stopped on numerous occasions for document checks with a registered UK licence, and I've passed one of the PT age limits for renewal during the period since I've been here.
With regard to registering vs exchanging, it was the case (but apparently is not any longer) that there was a massive backlog on issuing / re-issuing of PT licences, sometimes of well over a year, during which time you would be supplied with a document in place of your licence. The document is only valid on the roads in PT, which means you couldn't take your car into Spain or anywhere else, nor drive in the UK during that period.
The other thing is that registering the licence as opposed to exchanging is a slightly easier process, not requiring a medical, for example, nor photographs. Done and dusted in the time it takes in the IMT office. And free, as opposed to 30€, which the exchange costs. Always a bonus for skinflints.
I'm sure good sense will prevail over Brexit with regard to driving licences for those already resident. If a UK licence was issued when the UK was a member of the EU and has been registered, it wouldn't make sense for it suddenly to be deemed invalid. Once the UK stops issuing EU style licences, it might be a different matter but certainly not anything to lose too much sleep over, in my opinion. Lots of foreign licences from outside the EU are recognised and valid in PT - just slightly different rules about how long for and when they must be exchanged by.