In the light of the recently released cabinet documents from 1985, it is quite revealing that even 30 years ago there was doubt in one exam system for all. It is also quite telling that Keith Joseph education secretary (tory right winger) was the advocate of the GCSE system. It is also amazing that many in the education unions wanted to continue with O Levels and CSEs , this is the complete opposite way today.
I took GCSE exams in 1990. My school never took O Levels as it was a modern school in Kent ,so I suspect this must have been a cultural shock to them as well as the grammar schools.
I also think that the O Level exam system was created for the top 20-30% of ability pupils. The reality was it was created for a selective education system.
Nonetheless it is interesting to think that even before their introduction GCSE exams were creating debate about rigour and standards.