To those amongst us that have used the electronic toll Autoroutes in Portugal be aware that the authorities do keep records, have long memories and do check and enforce. Since the electronic toll system was introduced I have done my best to pay my dues and successfully most of the time.However when the system was first introduced it was theoretically possible for foreign registered vehicles to retro pay at a Post Office, this proved to be impossible.I then went to the expense of renting a transponder which worked until it ran out of credit without me realising, the reason I will explain later. To get to the point. yesterday I stopped at a services on the A28 north of Porto and was approached by a car from 'Vialivre' occupied by two officers(not police) armed with a computer who asked for my proof of prepayment, which I had. This was necessary because they could not find my details on the computer, which they eventually did.The upshot of this was that they discovered 6 unpaid tolls from the initial period in March & April 2012. No fine was involved but I had to pay the tolls plus an administrative cost for each journey which I paid by credit card, note that the old 'portagem' autoroute system will not accept UK credit cards. The reason that my original transponder ran out of credit was because my pickup is a class 2 vehicle because it measures more than 1.1m in height above the front axle, I mistakenly assumed that it would be the same as a car in class 1.This means that most 4x4's will be in class 2 which has the added consequence that towing a single axle trailer(or caravan) becomes class 3 and a twin axle becomes class 4. this applies to all toll autoroutes in Portugal. I assume they have some method of measuring this as every toll both, both manned and automatic came up as class 3 with the caravan. We are on our way back to France from the Algarve through Northern Portugal & Spain towing a caravan which we have found to our cost is class 3(car & caravan is class 1) making the journey very expensive as , for us,the autoroutes are the only practicable roads in our timescale,doubt if we will do this route again for a while. This not a whinge but a warning to those towing trailers and anyone returning to Portugal that the authorities keep records and do enforce.