I work in a Halfords and we seem to be the only store that doesn’t adhere to the gold/silver/bronze service tree. We do what is asked/required, don’t overcharge and often won’t charge for small stuff.
There are many of us with formal qualifications (Cytech etc) and they recently paid out for the top 50 stores to do a cycle technician training course at a training centre they set up. Only a pilot scheme so not fully accredited yet but we are assured it was more thorough than Cytech 2 + wheelbuilding.
One thing i would ask of you is IF you have an issue with Halfords service, deal with it instore with the manager first, as any complaint lodged via customer services just gets shunted back to the store manager to deal with anyway.
TL;DR don’t bother with gold/silver/bronze service, chances are all same.