@MacOS10 wrote:
OK, I've changed nothing on my old MacBook
And that is the heart of the issue; Apple also has changed nothing. Apple has not done their user base the courtesy of keeping root security certificates current on users' older devices.
The mitigation here (it is not really a fix) has been to down-grade the security certificate standard to accommodate the lack of up to date security fixes from Apple. You should anticipate similar issues should another service provider also issue security certificates strictly to current standards, as did Plusnet.
Superusers are not staff, but they do have a direct line of communication into the business in order to raise issues, concerns and feedback from the community.
