I have honestly had the most amazing experience with the upgrade team.
I fly on Thursday the 16th June and rang to start the upgrade process on the 2nd. I was informed I wouild recieve a callback with more details within 48 hours, got called back within 20mins, had my email sent off with proof of travel and application details 15 mins after that. Got an immediate confirmation email from the Peterborough upgrade team, followed by a 2nd confirmation email later on that day. (This was still on the 2nd)
Yesterday (7th) recieved an email stating they had recieved the request and noted date of travel.
Today (8th) recieved phone call stating I could pick up from my local passport office tomorrow.
Genuinely didn’t expect it, delighted!