The grading is done by a complex system called UMS marks. For the majority of exams, you need 90% for A*, 80% for A, 70% for B etc.
UMS marks means that papers or different lengths, practicals, controlled assessments etc can all be factored so that they can be counted on one scale.
However, the awarding of UMS marks are not directly proportional to the raw marks. In A-level, for most papers, you have to get 50% in raw terms to score even an E grade. Below that, you get nothing. It is very harsh on the weaker candidates.
I haven't done a mega analysis of where the grades are awarded, but I would say that there are more higher grades awarded than there are lower grades nowadays. I don't think it is the bell curve that it used to be. But this doesn't mean that there isn't a bell curve in the raw marks that candidates achieved - but just once you fudge in the UMS, the bottom candidates disappear as if they never existed, and it looks like there are proportionally more top grades.
Whether the courses are rigorous or not compared to yesteryear is a worthy thing to debate. But we have to be realistic about the content. In Biology in the past, you might have had to sketch and label the internal organs of a rat, but is that really a skill our young people need today? A-levels today are more about analysing and synthesising rather than recalling factoids.
I don't think I would want to go back in time. Our world has moved on. It's a bummer that grades then can't be compared with grades now, especially university degree classifications.