Dvla like to issue licences to anyone these days. This nutcase shouldn't be on our public roads, he's a danger and will cause a fatal accident one day.
To put people clear, this incident that happened in front of my eyes happened before this pic was taken on the B1257. This is more up on the moor as you can see. But before this stretch you are lower down on a section that is continually twisting with corners every few yards it seems and is narrower than this stretch and shrouded with trees on either side in places.
The lack of markings is due to the fact it is likely newly laid tarmac.
So whilst the act of leap-frogging as I have dubbed it (overtaking at speed consecutive vehicles) may not be wrong, where he did it with corners every few yards or so on a narrow road certainly is very risky to himself and to oncoming traffic. And I don't think my dad was driving too cautiously. He was not driving that slowly. The Dacia was overtaking cars much faster than our own. I looked back in the drivers side wing mirror to find an Audi Q7 next. When next I looked back it had become that Dacia who was very close indeed to the back of us. Almost tailgating us. So that driver had gone fast enough to overtake the Q7. He would go on to do it continually.
what you call leapfrogging is also known as making progress.
Looks to me like a pretty open road with good visibility.
It looks like a wide country lane with decent width carriageways and a dashed central line- I would expect this to be a national limit.
If this sort of maneuver was beyond acceptable limits, there would be a solid white line and/or a 50 limit.
finally, given the car is a dacia sandero and it overtook you with aplomb - chances are your Father was driving too slowly/over cautiously.