When you get a "you have seven days to respond" type letter and it only arrives three days after the seven days has expired then I would bet cash money it never actually got posted until a couple of days ago despite the date on the letter. I worked in a few civil service mailrooms when I was a student and nothing urgent happens with urgent mail. It gets handled in between breaks and if it doesn't get done today it might get done tomorrow. We would send out jury duty summonses and batches would be sent out when you could be bothered, not according to the court schedule. Nobody cared about the chaos it caused, "it's just how the system works". Even internal mail bound for that day's court sessions may or may not get there on time. I don't imagine any other government or NHS office is any more efficient.
Parcelforce on the other hand, I would much rather chance it to one of the courier services. In fact, I'd rather just kick it down the stairs and piss on it myself for free than have Parcelforce do it. But there doesn't seem to be anyone that does parcels well. Even the pricey ones like Fedex (or as Ricky from Trailer Park Boys calls it, Fuckex) are a gamble.