obviously not but the article fromDavid attaches a value of 0.5 bn to justify Royal Family.
“Brand Finance’s calculations show that tourism revenue connected to the monarchy and its heritage has been valued at £535 million for 2015”
I don’t have the ‘in-bound tourism cause breakdown data’ but I’ say that as a small part (0,5bn) of the overall 26bn
"But the UK’s tourism body VisitBritain states that while international tourism is Britain’s third largest service export, with inbound tourism to Britain worth £26.2 billion",
0.5/26 or 2% is a conservative believable figure.