This seems to be a hot topic in the news at the moment. When I decided to put in the application for my renewal (online, standard service) I was told to allow ten weeks for delivery.
In my case it took 2 weeks and 1 day.
I did use a photobooth that delivered the picture to the passport office (or allowed them to download a copy to be more exact).
The online tracking worked up until the point that the passport was printed and then seemed to stop updating (it was meant to inform me when the passport was passed to DHL for delivery to me, it didn’t).
Anyway… Maybe I was lucky but I’ve got no complaints about the service I received.
This seems to be some kind of issue here too (i.e. not only a UK phenomenon). I renewed my passport recently and it took 6 weeks to get myself identified (from the booking to the actual appointment) and another week for the delivery of the passport itself.
You need to visit the passport office if the fingerprints are last taken more than 6 years ago (meaning in practice every second time). That was the case for me this time.
The general explanation has been that a lot of passports have been expired during the pandemic and are only renewed now and in addition the current war seems to explain some of the recent peak (according to the news some passports are renewed well before the actual expiry date).
Application made jan 18, requested old passport jan 19, old passport receipt acknowledged jan 31, new one posted out feb 7. So it can be quick; delay seems to have been with posting the old passport to them, everything else was electronic.
4 weeks for renewal of mine and it’s a nice blue one ! they keep you updated on the progress so no complaints over the service, would imagine the delays come with first time applications, kids ones and/or where nationality/residency status is complicated