Also for @VanillaDaydream
The current appeals code states that, in considering the case, the panel must consider what the school can offer that the allocated or other schools cannot. This does imply that other schools can be considered. However, taking my example, let us imagine that there are three schools in the area offering Spanish - A, B and C. If we take the "only school" approach, an appeal for school A will fail, because schools B and C teach Spanish, an appeal for school B will fail because schools A and C teach Spanish, and an appeal for school C will fail because schools A and B teach Spanish. So our child, who really needs a school that teaches Spanish, remains disadvantaged.
My argument would be that the appeal panel for school A does not know if places are available at schools B and C, nor do they know the outcome of any appeals for those schools or the strength of the case to refuse admission to those schools. It may be, for example, that schools B and C are so overcrowded that no appeal can possibly win, so if the appeal for school A is rejected on the grounds that schools B and C teach Spanish our child is definitely going to remain disadvantaged.
Given the above, my view is that, whilst there may be some circumstances in which it is appropriate to consider other schools, in general the only schools in play should be the appeal school and the allocated school. I think there was an LGO decision to this effect once, but sadly I don't have the reference and I can't find it on their website.