is bolton school the biggest independant school in the UK?

Answer 1

1. Probably, though, unhelpfully, you have not explained what you mean by biggest.

2. There are two possibilities, as I see it:
a) size of grounds in acres ,
b) number of pupils.

3. ACRES
Bolton is nowhere near being the largest school.
a) Bolton claims to have "outstanding facilities set in 32 acres of grounds".
http://www.boltonschool.org/BoltonSchool/Globalinformation/WhyChooseBoltonSchool/
b) Stowe claims "magnificent grounds of 750 acres", and that's just one other school.
http://www.uk250.co.uk/frame/2690/stowe-school.html

4. PUPILS
a) ICS shows a total of 2,823 being:
(i) Girls' division: 1,533 (165 + 1,164 + 204)
(ii) Boys' division: 1,290 boys (1068 + 222)
http://www.uk250.co.uk/frame/2745/independent-schools-information-service.html
b) I can't any independent school with more pupils (though I can't find any reference to any independent school being the biggest either).