Any new annex would have to be from a Berkshire gs, as the entry exam is different in bucks.
That should not really be a problem. The bucks academy can have whatever entrance exam and admissions policy it chooses. The satellite just have to have the same as it would all be "one school". The fact that the satellite building is on Berkshire soil should not be a problem as long as there is a bucks academy grammar wants to do this ( is there one?) and it meets the tests for being a satellite and not a new school.
Interesting though. It seems that this is an entirely politically driven idea and not one that a particular academy has come forward with. Maybe this is also the case in sevenoaks. Rumour has it here in kent that high 6 figure sums of taxpayer money have been spent on grammar annex proposals including building plans and planning permission processes. But, "look no satellite" and a delayed free school building is the sum total of the result of this great idea at the moment here in kent. And another million or more to be spent on temporary classrooms for the delayed free school ( oh yes, the excuse now is "surprise " asbestos removal in the old school which has first to be demolished).
It is interesting that the politician in question is not also angling for a satellite of a bucks high school in Berkshire!
It's general election season of course. Some feasibility studies are not always what they seem. The options under consideration are never the full range in these politically driven vote-catching gambles.