Just spotted this, so thought that I would share it before you post anything off or lose out on your old stamp books.
I only purchased books of stamps recently and was given the old ones not knowing, insist on the new barcoded ones. Link below how to swap your old stamps.
"We’re giving you plenty of notice about this change and any non-barcoded stamps you have will still be valid until 31 January 2023. If you won’t be able to use all of your stamps by that date you can swap them out for new
barcoded ones
http://www.royalmail.com/sending/barcoded-stamps
You can request a form off them just add details if you don't have access to a printer or print out a pdf version.