Just adding: The 70mph speed limit definitely came in in 1965 though. The 'oil crisis' one you're thinking of was in 1973 when speed limits were temporarily set at 50mph for all roads. This time it WAS just temporary!
You raise some good points with regard to older vehicles. Not only were they much less safe than their modern counterparts (I believe road fatalities are now at about 25% of their 1967 levels, even with considerably more cars on the roads), but a lot of them couldn't get anywhere near 70! As far...
A pedant writes ... It was December 1965. Initially it was a 'temporary measure', but was made permanent in 1967. It was brought in after a string of accidents in fog. The authorities reckoned (rightly) that they were caused by people driving too fast for the conditions.
I think variable speed...