The UK has ruled it out as a solution for large local events and cultural activities, they haven't ruled out vaccine passports in general.

As far as I can tell they're still very much planned for inbound international travel to the UK, and they're already in use for outbound international travel - the NHS app is accepted as proof of vaccination status at the border when entering quite a few countries e.g. Greece https://www.gov.uk/foreign-travel-advice/greece/entry-requir...