I think it is expensive for parents to pay for transport in rural areas and if a local authority then says they will not pay for transport to the local grammar, only the local school, it does disadvantage the less well off, especially if they have more than one child. Lots of transport policies only work well for urban areas, but not rural ones.
By definition, the nearest all ability school, is not a grammar if the grammar children are 5 miles away in another school. Frequently subjects as Further Maths, Science A levels and a choice of Languages are missing, so these schools are not suited to higher ability children and, of course,do not get them (in Bucks) and they are not comprehensive. There is a big difference between the ability of level 5/6 children. They are not all the same which is why some do not get into the grammar schools even after coaching. The new 100 Mark may make it clearer who the top ability children are but even then, not if they have been coached for the tests. The children who are not coached fare the worst. If there are grammar schools, the poor have least access to them. Fact.