Although, as Dixie is aware, some of us look at the Law book, which places a condition on the restart that the opposition to the kicking side are all behind their 10m line
No it doesn't.
We have been here before, so you know my views. Law 13 is very badly written. It takes the trouble to distinguish kick-offs from restart kicks, and then forgets about the latter after the lonely mentions in 13.2. As a consequence, 13.4 merely deals with the position of the opponents at a kick-off, not at a restart.
Law 6.A.7 (a) says the referee must blow his whistle at kick-offs, but does not mention restart kicks. It is universally agreed that this means he does not.
We also agree that the opponents must get back behind their 10m line before joining in play, but why do we need to assume that they must be allowed to do so in their own sweet time?
If Law 13 was properly written, it would cover this point.
BTW you don't need a sanction under Law 13.4 because the referee will not (usually) start play until both sides are ready.