No, it's designed to maximize what they can raise without pissing off
too many voters. Even as it is, it's going to raise barely half a billion pounds, which is relatively insignificant in a budget worth hundreds of billions; but it's something, and something they (think they) can sell to their core electorate as a bit of token redistribution, when in reality it's just a cash-raising exercise.
If they'd targeted the really rich harder, it would have looked more consistent but would have probably raised even less (because, when a tax starts being significant, the really rich have the means to find ways to avoid it). As it is, it looks insignificant enough that the really wealthy will just pay it and move on.
