I think the important question here is: once they've got your face or ID, do they store it? Is this effectively forbidding pseudonymity? It's worth thinking twice about this in a country that is actively censoring mainstream political speech in its media.
The claim is that the data is "deleted", but there is no way to actually verify it is in fact being deleted (and the chances are data itself might be stored in say AWS which may have its own way of "deleting" data, such as in backups, caches, multiple regions etc (however they have their own legal process which may not allow data to be deleted in the event of a law enforcement request, and there's no way for anyone using the service to understand who is actually handling the data as it passes by their servers, which could be suspectable to interception etc)). Truth is, the data is much too valuable, and is useful for long term storage to know what somebody looked like or who they were when accessing content online. The UK has the RIPA so they could serve a technology notice for data to be retained and prevent disclosure of that fact. Apple was recently involved in such a request to disable advanced data protection, and the UK government is disgusted by E2EE and the very idea they cannot access every piece of data they like on demand, and wanted the entire thing held in secret.
So the reality is, assume everything on the internet is being archived, including any scans you do, and adjust the threat model accordingly. The UK government will absolutely be able to access this information and know all about what you've been doing if you're foolish enough to actually submit legitimate information.