I think you are probably correct J52, and it is to do with Tony Blair dealing with the crisis which befell the RF when Diana died. Assuming that the story told in the film was correct, Blair saved the RF from serious misjudgement of public emotion when they initially took the 'correct' stance after her death. At the risk of being controversial, Blair wasn't just about the Iraq war.
Maybe the Order of the Garter is returning to ancient traditions. So they've got Andrew, and now Tony, they are all set up for Johnson. A bit of rape and pillage and some mass slaughter? Perfect! Have a knighthood!