Im bit baffled maybe its different in different parts of uk.
we live in outer city suberb with a few schools have choice of like 8-10 but was told as theres a lots theres no catchment area or otherwise known as area of prime responsability for us.
my mum lives small rural town and they have strict catchment area for primaries even in small town.
its been 2years since went through primary admissions procedure.
but im sure we had a set deadline/date to respond and accept or decline the place.
we did all ours online. as completed application online.
also not sure if applicable but voluntary aided schools ie faith schools can usally decide their own admissions policy and the lea acts as go between between parents.
my eldest goes to rc primary where had to hand in supplemntry evidence form giving faith, baptsim certificate and copy of utility bill for address.
The admissions criteria for faith schools has pecking order.
it should say in your admissions for schools book pack or school prospectus.
think went something along lines of
1)kids in care
2)baptised catholics
3)siblings
4)kids of baptised catholic parent
5)baptised christians kids
6)other or non faith family but seeking and supporting a faith based education, they used to maybe have small quota for non faith.
some coes want evidence regular attendance in church and letter from minister.
at end of summer term they had settling in sessions and we had to respond to that by letter too comfirming attendance and had home visit by teacher.
I know legally you can defer until age 5 however our la clearly says a place can not be held open for 6months we risked losing our top school as was oversubsribed.
good luck hope you get somewhere with it.