Hmmm. What is a 'partially selective' school? Community primaries aren't selective, are they?? I can see that in a selective school there is a problem - but secondaries don't usually have a siblings policy, anyway, do they?
So i simply don't understand this.
RE siblings in ordinary primaries...of course siblings need to go to the same school because of pick-ups etc, BUT I think that if a family get into a hugely over-subscribed school with thier first child, and then 'co-incidentally' move away but continue to send theri 3 subsequent children, it should be looked at. The over-subscribed school near me had almost NO 'proximity' places available last year because of the families who rent or buy close to the school for the fist admission and then move somewhere less 'edgy'. Then the flat they bought / rented is used the next year for exactly the same purpose, and the population of non-catchment siblings just grows and grows -and the families who live permanently in the area have to send their children to a school much further away across busy London roads.
But the rest of the country shouldn't have to suffer because of London-Schools-Panic-Madness!