Hi Janet my apologies for my tardiness in responding to this enquiry,
My understanding of the situation regarding this may be very much out of date and may have changed as the knowledge is several years old and I haven’t yet had the time to update myself.
From when I looked into to it, The Code Club was an unrelated initiative that fell into the overall remit of what the stem.org.uk was trying to achieve. The programme seemed reasonably agnostic as to what stem activities are run and merely provided a resource to enable stem related activities to be run by different organsiatiosn/schools/teachers etc and connect with stem ambassadors and volunteers. As part of that remit stem ambassadors that register are interviewed and have a background check done so it is known that it is safe for them to work with children, there is occasionally an optional extended interview with some training included in basic safeguarding principle. This provision is handled by local provider that I presume are contracted for the service.
An additional advantage was that at the time i was investigating a DBS/CRB check performed by an organisation such as an employer or school was not transferable and the cost of that check needed to be incurred again and the checks performed again for every organisation. The stem ambassador programme organised and performed the checks in a way that was essentially transferable as volunteers are recruited by different schools etc via their database. So the DBS/CRB check only needed to be done once even if the volunteer was going to work at several schools since the school did the recruiting and first contact via the stem/code club system.
As such the code club was leveraging an existing system with wider objectives and was able to do so because it fell with the remit of it’s activities. I would assume this was done formally rather than informally.
If fixers were to work with schools doing after school repair clubs then I would assume we could leverage a similar system. First get the fixer registered and checked as a stem ambassador and then recruited via the system as a volunteer to go to the school. Note the school would also register as a venue and go through the system to recruit the volunteer,
If as I hoped would be the case science or design and technology teachers were going to train up as fixers or deliver a fixer syllabus to their own pupils and students, DBS/CRB checks would already have been done internal to that organisation and the stem ambassador system would not be required.
I hope this helps a little but suspect its nothing more than what you may already have known. I’m not in a position to categorically confirm how the relationship was set up between code club and the stem ambassador programme or if it still runs in the same way.