thanks Ora, that is helpful, I hadn't seen that so the information about the 3 mile priority zone is important, but it also means that someone who is 3 miles into deeper Kent will be treated equally as someone who is on the Kent/London borders.
I was going on what was on their admissions page at
https://www.twgsb.org.uk/269/year-7-admissions which stated : "KCC will offer us 300 pupils for National Offer Day and at that point we will allocate places by distance to either the main Tunbridge Wells or the Sevenoaks site. Where it is possible we will then offer students the nearest site to their home address. We will only allocate site places once we have the list of boys to whom we are going to offer a place." which seems to imply that there is no 3 mile priority distance.
I think the two sources are potentially contradictory.