This may impact some owners:
Calor Gas discontinues its 4.5kg butane cylinders - Practical Boat Owner (pbo.co.uk)
Update 12 April 2023:
Looks like they have changed their mind, from the Cruising Association.
"⚠️Member Alert⚠️
Calor Gas has decided to continue exchanging and refilling its 3.9kg propane and 4.5kg butane cylinders for the immediate future.