fanny, Scotand has a significant history of allowing deferral - in fact for deferral to be a) quite common and b) something seen to be educationally advantageous by parents.
In England, until recently, the push has been to get children into school, or school-like pre-school settings, early to 'give them a head start', and deferral has been rare, esopecially because essentially a child deferring for a full year had to enter year 1 not Reception.
This is changing now at primary entry age, with more summer-borns deferring. HOWEVER, IME this change has not fed through to the primary - secondary transition, with it still being very unclear whether the child has to skip Y6 or Y7.
f considering deferral, ALWAYS establish the likely secondary school's policy on out of year admission first, before making a decision. i have taught a year-deferred child - but we had documentary evidence from all future schools that the change of year would be honoured at all transitions (3 tier system) BEFORE we made the change of year.