Advertising for panel members tends to be local:
1.12 Admission authorities (or a body acting on their behalf e.g. if the local authority manages the area’s appeals process) must advertise for lay members every three years. Admission authorities must place an advertisement in at least one local newspaper and allow a minimum of twenty-one days for reply. Admission authorities may also use other ways of attracting potential members, for example by issuing flyers in local newspapers or to local companies and community centres, and advertising on the internet, making clear that training will be provided.
The Code of Practice also states:
1.4 Admission authorities must ensure that every appeal hearing consists of:
a) at least one lay member. Lay members are people without personal experience in the management or provision of education in any school (though it is permissible to use people who have experience as governors of other schools, or who have been involved in education in any other voluntary capacity); and
b) at least one person with experience in education, who is acquainted with educational conditions in the area, or who is the parent of a registered pupil at a school.
I would have thought the majority of panel members are likely to be locally based, or to have become familiar with local conditions through hearing previous appeals. However, some admission authority areas can be very large, in which case not every single panel member will necessarily be familiar with all
of the schools, although it's quite likely that someone on the panel will be.