That's not quite what we did.
Firstly, I'd not filled up in Dublin, because of the price of petrol there: what with the way the Euro has risen against Sterling, it was definitely not cost effective to try to buy it there, so I was waiting till we got back to Holyhead. But we didn't spot a filling station at Holyhead, and the new A55 misses all the villages as it crosses Ynys Môn. So, finally seeing a sign for services, we dived off down to Llanfairpwllgwyngyllgogerychwyrndrobwlll
We then rejoined the A55 to cross the Menai Straits, but then got distracted again, because it was still daylight (the advantage of the earlier ferry) and I had this urge to go hunting the place where my family used to stay on holiday when I was a child. That's on the London Road - the A5. So we dived off down that road, which is deeply scenic, passing Bethesda and other small villages. Somewhere just beyond Betws-y-Coed, I think I recognised the turn (and I'm pretty sure that here is the actual place). (Somewhere about this point, I picked up a black van behind me, which followed me as far as Birmingham.) So we ended following the A5 down to where it becomes the M54, and followed that till it reached the M6.
(The thing about coming in on that road is that it's a little too far south for the SmartNav to consider it worth using the M6 Toll. So we drove down past Birmingham with much of the distance being roadworks, and an even larger distance being driven past a stationary queue of northbound traffic. Coming down to the M6/M1 junction, we saw signs warning that the A14 was closed between junctions 3 and 7. This would appear to be a regular overnight occurrence, since there was a signed diversion taking traffic a number of junctions further down the M1 before hooking back up the A45 round Northampton. But SmartNav reckoned that wasn't particularly sensible for us, since we are going to a point south of the A14, and going north back up to it, along it, and then south again is a bit round the houses.
So it was guiding us down the M1, and then taking us across via the A507.
then we hit a problem. Because the A507 was also closed, eastbound from the A507/A6 junction, and the SmartNav didn't know about this closure (it was a signed diversion), and it tried to guide us back to this road. Not good. Eventually, we got a route up to Sandy , and got round it, but the result of our scenic excursion via small mountain roads, stopping for a meal and some shopping, and having two east-west roads closed was that we didn't get home till 22:00, which is only about 2.5 hours earlier than previously.