The experiment took place from October 1968 - October 1971, during which time the clocks remained on British Summer Time.
It was before my time. My mum remembers the mornings as being dreadfully difficult and depressing.
What people often don't consider is that in the depths of winter, it's dark on the work/school run in the mornings and the evenings whether you are on BST or GMT. It only makes a difference when you are on the curve towards or away from the equinoxes. We already skew this towards lighter evenings - we have 5 months of GMT and 7 months of BST.
Where I live, the day before the clocks change, the sunrise will be at 8am and the sunset at 17:40pm. This then changes to 7am and 16:40 on GMT. If, say, you stayed on BST because you wanted it to be light at 17:00, you'd get approximately three weeks before it was dark again at 17:00 even on BST, and then not light until nearly 9am.
So you are getting darker mornings for very little benefit.
Added to this is lighting costs - most people have to get up at a certain time in the morning, and if it's dark, they need to put the lights on to get ready for work or start working from home and so on. However, in the evenings you have the option of turning the lights off or using lower lighting, watching TV in bed with no lights on, if you want to save on lighting costs.
We are never going to have the sort of climate where people want to be enjoying a long evening outside in winter, it's too cold and damp, lighter evenings are not much use if you want to be indoors anyway.
If I had my way we'd stay on year round GMT, but I think the system we have at the moment is the best compromise for BST fans.