"Given the last remotely left wing Government left power in 1979, and that during the last 40 years i can only really recognise perhaps 5 or 6 years of that same "left wing government" [...]"
The Comprehensive School system was a dismantling of the 1944 Education Act's tripartite secondary system. The first casualties were the Secondary Technical Schools in the1960s - many of which had equal 11+ selection criteria to the academic High School's and Grammar Schools. The Secondary Technical Schools' higher running costs for additional specialist teachers and equipment was undoubtedly a factor.
That change was principally a 1960s Labour policy of Harold Wilson's Government. However - there were many in that party who saw the 11+ selection, albeit flawed, as a valuable vehicle for working class social mobility.
It can be claimed that the Comprehensive inertia was unstoppable by 1979 - with Local Authorities committed to the change by then. The amalgamation of schools into larger units offered potential economies of scale at a time when the country had an economic crisis.
In spite of Margaret Thatchers personal faith in Grammar Schools she did little to promote them. Her Government replaced the GCE 'O'Level and CSE by the GCSE in 1988.
The education problem remains the same as it has been for a century. How to provide an education that allows a child to reach its potential - and provide a suitable workforce of adults. The economic obstacles have been how combine the ethos of a small school with the cost of providing good teachers in a wide range of subjects. The final, and most important, factor is instilling the general population with the importance of their children being educated.
**Declaration of vested interest:
I am a working class lad who benefited from an 11+ Technical School Education through to "A" Levels. It was one of the last boys' Technical Schools to be turned into a larger mixed Comprehensive in 1970. It subsequently served a much smaller parochial area rather than the whole city. From the anecdotes of teachers and pupils there was then a decline in discipline, academic rigour, and extra-curricula interests. The technical and science subjects became less intensive too.