Hmmm. I have found myself in exactly this position - with an OH who works very long hours out of the country for 45weeks a year and who wants to spend some of this money on an education for DCx3 (5, 3 and 1)
Last week he visited and I checked if he still wanted to pay for them to go to school. It's a yes. The school takes them from yr3, so that's in just over a year's time.
I spent so long wondering whether private education was possible, and now it seems it is I am spending much of my time wondering whether just because we can, we should.
I disagree with the stuff about wanting DC to meet children from all backgrounds. I was state educated (as was OH) and I didn't meet children from all backgrounds. I met no one who was the child of a doctor, barrister, financier. I played with no one who was the child of a drug dealer, prostitute, blacksmith (to my knowledge). I think at private school, these parental occupations would be in evidence 
Please try and convince me that spending my Wonga on private education is a Bad Thing. Because I am struggling to equate the principles of my 20s with the reality in my 30s.