These are questions Harry & Megs should have considered before making their seemingly hasty poorly planned exit from the RF.
If Harry returns to this country, and while he is with other members of the RF, he will receive the same high level of protection as them. It is the times when he is out and about pursuing his own projects that he is demanding UK funded protection for.
It seems to me that he should pay for this himself, or ask his Granny or Dad to pay for it. He must pay for his own protection at all his high profile appearances in the US, where with their lax gun laws he must be at more risk than in the UK. So he should do so here also.
I don't think that he realised all the implications and results of his decision to leave The Firm, for instance at first he hoped to still do foreign tours, and to keep his honorary military appointments.
So no doubt the way he has been stripped of privileges that he had been entitled to all his life, has come as a shock to him.
But he made his choice, and now must live by it, and pay his own way, with private self funded security.