For the Cambridge (CUSF) launch last month, the permission also had a new requirement for Swanwick (45 mins before). We're used to having the requirement for our central London launches (15 mins before), but it was new for a Cambridge launch.
The issue with including Swanwick with all launches (if that's what they are doing) is we've had a real mixed back of controllers over the years... There doesn't seem to be a written down procedure for them to follow with balloons, instead solely down to if they think a balloon is risky or not. Had some excellent controllers that gave thumbs up in a few mins, while others have taken 30-45 mins and numerous calls back to finally get thumbs up (or in 1 case, thumbs down as they didn't feel they could approve it as it *could* float in the path of an aircraft...)
In the case of the CUSF launch, it ended up delaying the launch as they also couldn't find the paperwork on their end (which is pretty typical from experience).