Bear in mind that, usually, the person would have been born with that name so it's not just one that would sound good at a certain age.
And all three have strong British connections. I'd go for Robert, simply because I think it sounds better with the surname, but maybe try and think from the parents' point of view, or whoever named this character in the story (if this is for a story, sorry if it isn't). Which would they prefer? Maybe it was a grandfather's name or they liked stories of King Richard or Robert the Bruce or love Sir Robert Moore?
Richard sounds most British, but Robert is more of a child's name. Maybe you could make Richard have a nickname like Richy, making him sound yuonger.
Good Luck xx
Richard sounds the best. It's an old English name. I think Richard Reed will be good, sounds posh, and it is the best name on there for it. You can shorten it to maybe Richie or something.