There was no appetite for Scottish independence in the 70s.
The SNP certainly polled well in 1974. Whether there was "appetite" or not is beside the point. (It's true that Scotland is much nearer indepdence now than it was then.)
The point is that the UK government feared Scottish independence and went to great lengths to conceal North Sea oil revenue and Scotland's potential as an indepdenent country. Now we can actually read it in government documents in black and white.
While in public the government played down North Sea oil, in private their report advised:
The country [an independent Scotland] would tend to be in chronic surplus to a quite embarrassing degree and its currency would become the hardest in Europe, with the exception perhaps of the Norwegian kroner. Just as deposed monarchs and African leaders have in the past used the Swiss franc as a haven of security, so now would the Scottish pound be seen as a good hedge against inflation and devaluation and the Scottish banks could expect to find themselves inundated with a speculative inflow of foreign funds.
http://www.oilofscotland.org/mccronereport.pdf
The report was kept secret for 30 years.
In 1974, McCrone wrote a now-famous report for ministers predicting Scotland would become "as rich as Switzerland" if it controlled North Sea oil - a prediction that was kept from voters.
http://www.heraldscotland.com/news/13159881.Exclusive__McCrone_2__
secret_report_which_advised_Westminster_to_set_up_oil_fund/
Dennis Healey who was chancellor in the 1970s said:
I think we did underplay the value of the oil to the country because of the threat of nationalism but that was mainly down to Thatcher.