Thanks very much for all the posts, giving both some pros and cons.
ampere, yes it is a Major League sort of school, although not Premiership. The fees for day pupils are considerably more than £11,500 pa, let alone the boarders!
elvis, I better not say where I am (paranoid). There are state options, but too competitive to be relied on.
Pugs and others, I am sure my own insecurities are affecting me, having felt somewhat the poor relation in my own private school. Having said that, I am also sure that my education gave me great benefits. DH went to more of a Major League type of school, but from a more stable financial background, so he doesn't have the same worries. His are more focused on the practical issues as to how we would manage if I lost my job.
Bluey- the children are still too young to be consulted, it's down to us. It is the sort of school that I would choose in the sense that it has the usual benefits of a public school- small class sizes, excellent facilities etc. My main feeling is that the children would have a greater chance of achieving their full potential as individuals there, be that art, music, sport, academics, whatever. The state junior school they currently attend is also excellent (lovely children, middle class pushy parents, dedicated staff), but having helped out there I do feel the teachers are up against it with class sizes of 30 plus.
Runout, yes the boarding thing is as much a concern as any. The day pupils are in a minority, and a good number of the boarders are from overseas (although this may help with regard to the wealth thing, as the children just wouldn't relate to Russian/Chinese billionaires!). We know quite a few ex boarders and they mostly say "don't be a day pupil in a boarding school".
Roisin, it's not really possible for us to save up for secondary for practical reasons, although I can see the logic.
Well, if anyone has managed to get through all this and has any more advice, please go ahead! Thanks.