@Bryonyshcmyony,
'The schools would be rubbish within five years if they had to constantly adjust to please various wealthy and litigious parents'.
There are a few famous public schools with long waiting lists (St Pauls, Wesminster, Eton, Kings etc) who can do what they will, as if parents pull their children out, there will always be another waiting to take their place.
However, the vast majority of fee paying schools do accommodate what, on average, the parents want from them. It does not make them 'rubbish' as most parents want good grades and well rounded children anyway. However, it probably does make them more likely to 'spoon feed than state schools. This is part of the reason why state school pupils with identical A level results do better than private school pupils in their degree classification (this is a fact, which I can evidence if you like).
'The vast majority of independent school parents maybe wealthy but aren't litigious and trust the school to do a good job'
On the whole, I would agree here, although I might contend with the word 'vast'. Most parents are lovely and leave the school to it. However, it only takes a minority to influence a school. Litigation over grades is a time consuming nightmare for schools. They would rather overstate grades a bit (not ridiculously, to make themselves look foolish) to avoid it.