Although 5 GCSEs (with fairly low grades) are all that's required as minimum entry to integrated flight schools, to have any chance at a tagged scheme you'll almost certainly need a few A-Levels. Maths and Physics are the most relevant. I'm not sure what I'd suggest for a third one as I don't know what the English system offers (and therefore what's expected of you), but I'd imagine you can't go wrong by studying English or perhaps getting another science under your belt. Just don't do A-Level cake decorating or something.
But remember, you can work; improve your education; and train all at the same time. It's hard work, but it's possible if you are very commited to it. But why wouldn't uni be an option after A-Levels. I thought that was the idea of A-Levels in England?