Harry will still need security whether he is Harry Mountbatten Windsor or Harry HRH /Duke /etc . Stii the Queen's grandson and brother of the next King .
But why, if he is no longer a working royal? If the argument is that he's the Queen's grandson, then surely all the grandchildren require protection, which doesn't seem to be the case. If the argument is that he is the brother to future King William, then why doesn't the US, say, give the siblings of sitting presidents secret service protection? Or the Met give the siblings of current Prime Ministers police protection?
The only argument that seems solid is that he gets protection because he is the son of future King Charles, and I think this is a reach. Charles is not the Monarch yet.
As a working royal, of course there is a need for police protection because an individual is acting in loco monarchis, but otherwise?
I think it is worth pointing out that there's a model for how much this could all cost with Tony Blair. He is reported to have cost ( and still cost) taxpayers millions in police protection with his global travelling (it was £250K pa back in 2010 when he was largely British based).
The Daily Telegraph in 2016 reported that Blair's lifestyle (jetting around the world as envoy, mingling private business deals with charity work) meant he had up to eight officers with him on international trips, with four stationed at his homes and the salaries were roughly £70K pa each. And that didn't include the cost of their travel and meals. The estimate was that it cost the taxpayer upwards of £840k a year.
And he's just one person. With Harry and Megan, you are looking at possibly double that if they often travel separately, and then there's Archie to consider.
I think police protection and the royal family needs revisiting. It is said that personally protecting the entire Royal Family, their associated residences and escort needs takes 1000 officers.
And at a time when our ward only has one PCSO on a pushbike to cover 25 square miles and 5000 households.