Ok lots of speculation
Co-Ed options...
No mention of Brighton College (probably too academic)
Or Sevenoaks (IB and other side of town)
Wellington agree too trendy
Marlborough is an obvious option
Oundle out of the way but honorable option and in some ways good if it is out of the way
Boys only
Westminster, Eton, Tonbridge - he would really need to pass the exam
Dulwich would need to pass the exam and too many day pupils
Caterham, not familiar
Kings Canterbury - why not, nice school and near one of their places
Rugby? Not posh enough?
2nd tier posh boarding boys:Harrow, Radley...
So not a lot of choice for Co Ed boarding really (for them high profile posh ppl at least!)
(End of speculative post)