Hi Brocky!
Saw your plea on you-know-where and thought I would pop in and offer some moral support.
A balloon over the Palace? I was stood on the platform at SE7 at 0430 zulu and didn't see one. The planes were happily swooping into LHR.
I did a post some time back and was informed that planes have to keep a height of 4,000 feet over Greenwich due to the poximity of LCY, so my guess is that the balloon was too low to cause problems.
That's a guess though.