Many of the sub 70s in the U.K. were created before the modern definition of par.
Most courses in the UK were built before the Great War, when the stroke system generally used was "Bogey".
Although almost identical in concept to "Par", "Bogey" was calculated with the equipment used at the turn of the 20th century in mind, while "Par", originally a Scottish invention, was codified by the USGA in 1911 as follows;
Up to 225 Yards Par 3
226 - 425 Yards Par 4
426 - 600 Yards Par 5
Over 601 Yards Par 6
"Bogey" would have been calculated along very similar lines, but far more discretion was given to individual clubs. The parameters of "Par" evolved over the years as technology advanced, while "Bogey" tended to stay as it was. The main difference was at holes in the 400- 450 yard range. These became Par 4s but remained Bogey 5s.
"Bogey" remained the predominant system in the UK until the 1950s - later at some more traditional clubs. Most current courses therefore, would have been designed with Bogey in mind rather than Par. A course with a par today of 68 would typically have had originally a bogey of 72 or 73. It would not have been considered particularly short or of failing to meet any desired threshold.
The modern day definition of "Bogey" as meaning a hole played in one shot over par is an Americanism which was greeted with much annoyance by the British golf establishment at the time. I can remember my grandfather still harping on about it in the 1980s!
A good summery can be found here;
http://www.scottishgolfhistory.org/origin-of-golf-terms/bogey/