As countries across Asia, Africa and the Caribbean began to fight for independence and decolonization, it was inevitable that the former colossal British empire would suffer. The British could no longer count on unfettered access to the natural resources of countries they colonized and brutalized. In addition, the British faced competition from other emerging countries that recovered from World War II including Germany and Japan.
The exact years of the decline of British industry were not inevitable. Certain policy changes could have moved the window of decline earlier or later, but the eventual decline itself was inevitable. A huge part of British industry was based on colonialism. Raw goods were imported cheaply, and finished goods were exported to a market that had little choice but to by from their imperial overlords. The collapse of colonialism after WWII combined with increasing wages in the home islands (compared to the much lower wages in developing nations that suddenly had infrastructure investments) made the eventual decline of British industry inevitable.
It would seem industry has some sort of a bell curve when introduced to a society or country. It grows, does really well, then tends to slack off. For this reason, it was probably inevitable that British industry declined in the 1970's and 1980's. While different tactics may have changed the dates, I have my doubts it was stoppable.
I think that it was inevitable that the British industry declined in the 70s and the 80s. All signs seemed to point that it was only a matter of time till the industry in Great Britain would face a major problem. I do think that it has made a great comeback today and can only get better.
No, it was not inevitable that British industry declined in the 1970s and the 1980 declined, because the British people were still the same hard working, developing people that they always were. What changed was that union bosses demanded outrageous things, and the businesses couldn't keep up. That could have been controlled better with free market priorities.