When you have a problem set as complicated as the current state of schools admissions, to state schools in London, the trick is not to try and solve it all at once, but to see if it is possible to break the problem up into bits, and then try to work out which bit to fix first - what the correct order would be.
What we have in the case of Crouch End, and not to beat about the bush, Coleridge, and (possibly it seems, Rokesely,) is a suspiciously high number of siblings. In the case of Coleridge, over half the intake with well over half of the siblings living further away than the last child admitted on distance, and with ten of them living over a mile away. The admissions radius this year being just under a third of a mile.
There will be cases where parents really were resident at the address that got their first child into Coleridge, and have now moved away from Coleridge for understandable reasons - for example if they were in a two bedroom flat with the first child, but then have a second child and move for more space.
BUT
There are persistent rumours of people "doing an Eleanor Palmer" that is renting temporary accomodation near Coleridge for the right period of time to get the first child in, then moving back to their long term address and relying on sibling preference. Deleting sibling preference will catch those people out, should have the effect of reducing the average length of journey to school, it seems sharply, and make school run motor traffic less of an issue...
It will also increase the admissions radius for Coleridge.
ALSO from the point of view of the school places problem, it will mean that a much better picture of "real demand" will appear.