I think Boz is correct about the 'blocking' aspect. I believe there is a certain 'etiquette' that if the outgoing PM doesn't accept the kick upstairs none of the others can be offered it until that PM is offered it or dies. Presumably this vacancy was created by the death of Prince Philip and that's why Blair could be offered it so that Brown, Cameron, May can also be in line for Honours. I wonder if Brown would accept. Perhaps he will be offered the Order of the Thistle. The Order of the Garter is limited in numbers and is a personal gift of the Sovereign. Perhaps the Queen, who saw Blair as PM on a regular basis, knows more about his contribution than others.