Sorry for late response but I knew that I had seen something about it in addition to what Lownie had reported on, and as is often the case with these things, it was Private Eye who got hold of the story, but I can’t find a date for it,
“The appointment of Andrew to replace the Duke of Kent as Trade Envoy was vigorously promoted by none other than Peter Mandelsohn, then out of government after his second cabinet resignation, but still with the ear of Prime Minister Tony Blair. Blair overruled the principal opponent of the plan - none other than Andrew’s big brother. Brian thought it wrongheaded as he suspected Andrew would use the post as an excuse to cultivate friendships with the wealthy, chase women and play golf. It would certainly be interesting to see the notes revealing why Blair ignored His Majesty’s sage advice at the time.”
NB Private Eye’s nickname for Charles is Brian
So to be fair to Charles it looks like he was overruled twice!