In the 2025 Statutory Guidance To Police Document for Firearms there is a requirement in Section 4 with regard to section 4.4 about changes; "including any recent changes in the certificate holder’s mental health or life circumstances." this can impact the persons ongoing suitability to own guns.
4.4 If any new information or intelligence is received relating to domestic abuse, violent conduct, or any of the other most serious matters as described in Chapter 3, or any incident that results in the surrender or seizure of firearms, a full review of the certificate holder’s or RFD’s suitability (and not merely the most recent incident) must immediately take place. If a certificate holder is involved in a violent or abusive offence or there is an allegation of domestic abuse, consideration should be given to interviewing the certificate holder’s partner, ex-partner, family or household members in confidence about their relationship with the certificate holder and any domestic issues or other concerns they may have, including any recent changes in the certificate holder’s mental health or life circumstances. New information or intelligence about other serious matters should also result in an immediate review at the chief officer’s discretion (noting the requirements of paragraph 2.16, above).
I would argue that a simple cancer diagnosis is not enough to revoke a persons SGC and that maybe Section 4.6 would apply.
4.6 Where there is evidence that a certificate holder or RFD presents a higher risk but is not considered to meet the threshold for refusal or revocation, home visits or inspections, interviews or other follow-up enquiries are justified so as to check on the certificate holder’s continuing suitability.
The real question is the actual medical diagnosis and maybe this is a GP overstepping their position.
Full document can be found here:
www.gov.uk