"Why do some people think £20/25 an hour is expensive?"
If £25 an hour for tuition (per subject, per child) is cheap, why don't all parents employ tutors for their children?
Why do so many children in this country get very poor results in essential subjects like Maths and English?
£25 an hour might be cheap for some, but it is unaffordable for many.
"Why should a qualified teacher charge less than that?"
Why should a qualified teacher be tutoring in the first place?
If the 'qualified teacher' is any good in class, very few of his/her students would be needing tuition.
Is a 'qualified teacher' in our 'First World' country not paid a 'professional' salary so that he/she finds it necessary to earn extra money after school?
Or do the 'qualified teachers' find it more lucrative to give up teaching and do private tuition instead?
"People pay a £100 for a letter from a lawyer for example."
Most not-so-rich people in this country don't.
"Personally, education is high on my value list."
So would you pay £25 an hour for tuition so that your child would get an A* rather than an A or B without tuition?
Would you pay £25 an hour for a 'professional' maths tutor to teach your child tricks to get an A without understanding the questions?