Issymum, that is so sweet about the Home-ec teacher offering to alter the uniform! My sis has a little shrimp starting reception at a very posh central London school (with unifom to match) in September. Shrimp nephew is still in mini-Boden age 2-3 and looks like a little baby mole in his blazer and cap!
Agree about the silly uniforms, tho' actually I'm slightly schiz about it. On the one hand, I have a sneaking fondness for the whole 1950s Christopher-Robin-meets-Rachel-Riley aesthetic (in contrast to the Woolworths/B'wise aesthetic of my kids' primary school) but it is deeply pretentious and the practicalities of it would hack me off massively.
Interestingly around here (champagne socialist Islington/new Labour Hackney) the private schools either have no uniform at all or go for something generic that could pass for a stateschool to the uninitiated. So I think the uniform does tell you something about the kind of parents the school is trying to cater for.
I would also suggest that you use the Ofsted website to identify the three best (state) primary schools in your area, and go to visit them. The differences are illuminating and may help clarify what it is you want to be paying for.
Another thing to watch out for when visiting schools is that they will almost always pick the exercise book of the class genius to show you. This is done so subtly that you may not realise it's happening, so it's worth wandering round and looking at several to get an idea of the range of achievement. The private school I almost transferred by dd1 to was the only one where the headteacher didn't pull this trick. In fact she riffled right through the pile before commenting, "This child could hardly write when she got here, and now she's almost as good as the others."
A good question (particularly for pushy London schools) is: "How do you get the children to achieve their best without putting them under undue pressure?" That was one of the few questions that generated really revealing answers for us.