Never concerned with Jet Blast... and I am sure that LHR Director is a profesional of the highest order but....
"Some" airlines have very strange ideas indeed, and the best way is to query the OPS department to find the answers. Therein lies the problem, he may well not find a suitable or rational explanition...not surprising from a British aircarrier...and some (all) of our American carriers as well.
Still, if they want to hold, why not further from LHR, so as not to disrupt traffic?
Surely a "penalty box" can be devised for these guys.
It's called, "don't call us we'll call you".