I would say that the post-war boom came to an abrupt end in late 1973, when the price of crude oil went from $3/barrel to $11/barrel between October and December of that year; that and the OPEC- inspired embargo on countries supporting Israel in the Yom Kippur war. For a start, it spelt the end of the steam turbine - propelled ship, of any size. I can remember, in the company I worked for, all the 35,000 to 100,000 - ton dwt tankers went very rapidly for scrap, between the middle of 1974 and the middle of 1975. There was aclass of 65,000 tonners; the two steamers went then, whereas at least one of the three motorships lasted until 1982.
That being said, Britain had long-standing economic problems, stretching back at that time for around 100 years, and no - one in a position to do anything about it, actually bothering. That goes for politicians, of all parties, those in charge of the companies concerned, and those who ran the trades unions