I agree with you bibbity that the system does not work in cities, particularly London.
People live in an area where they think the schools are good - if they can afford to. This makes other areas suffer and results in a segregated community.
In some areas people cram into tiny flats for a year to get their eldest into the right school, then move down the road where property is cheaper. I know a lot of people who have done this. It's sneaky and wrong - but they don't consider there is an alternative.
Some say 'we moved here because the schools are so good we don't have to pay for private schools'. This is about more than handing down school uniforms and convenient parents evenings. For a family of 3, these people save £300,000 and meanwhile they are investing in their property.
As a by-product of this divisive system myself, I know first hand how it affects not only communities, but individual children who consider themselves as 'left behind' as their posh pals move away in year 4. Twas ever thus.
I think they are considering a lottery system in some areas - there has been a pilot in Brighton I think. And now we have Free Schools to make the system even more divisive.