Of course none of this built in rust would have had anything to do with alternating strike days throught the seventies...
Coal dug on Monday would sit outside until loading on Wednesday. It would then sit on the train for three days because no one could drive it. Then, after the weekend, it would finally get delivered the following Wednesday.
Same story with the iron. And then the steel. And then the panels... you can see where I am going with this 
I suspect that you could strain tea through the panel surfaces prior to actually welding them together 
Having known many, many people who worked at the factory that now produces the BMW Mini, it's not hard to see why British cars of the 70s and early 80s were utter shite - despite a usually good initial design.
The whole attitude was wrong, and the management did buggerall to weed it out. The phrase that Clarkson uses for BL workers, "that'll do", is far too kind. Damaged panels would go on. Panel fitting was rushed and often ill fitting. Corners cut. Terrible.
Fortunately, Austin Rover then teamed up with Honda, and there was a big change in attitude, and that showed in the cars that started to come out, such as the R7 Rover 200/400 series. Sadly, come the early 90s, BMW bought what was then Rover, and never invested in anything (BMW wanted BL's mass manufacturing techniques and 4x4 technology, not a car manufacturer). Then some of the original Austin Rover management bought Rover Cars from BMW for a quid, and that ended as expected, as the old mentality came back.