With effect from 31 January 2023 stamps that say 1st or 2nd class will no longer be valid as Royal Mail are changing to barcodes. After that date post will be treated the same as if its unstamped and charged accordingly. It is possible to swap stamps that you already have for the new ones though. Just flagging this up as I assume that no one will want to get stuck with an expensive book of useless stamps. Why they couldn't just accept them until current supplies are exhausted I don't know.
www.moneysavingexpert.com/news/2022/02/anyone-with-stacks-of-stamps-at-home-has-less-than-one-year-to-u/
To think that London, or anywhere else for that matter, does not belong to any one demographic