My DD is in year 8 at a London independent day school. She's had some serious friendship issues in year 7 and year 8. She has asked us to consider boarding schools as an option for year 9 (so in September of this yr) 
Aside from the whole issue as to whether boarding school / changing schools at all is an answer to her issues - how likely would any school be to consider her when their lists were closed months / years ago? The entrance exams are either over or incredibly soon.
By way of background, she is at a large academically selective school and is in the top 5% I would say in that school. So we would want her to go to a school that was suitable in that regard I guess (but they would be very sought after).
She's quite sporty, mature for her age, academically high-flying across the board, arty but entirely without musical ability. Any schools (either single sex or co-ed that spring to mind) within a couple of hours of north london - that spring to mind - all ideas gratefully accepted ...