If a garage hasn't signed up to the code, ask yourself why they haven't. Perhaps they're about to, but perhaps they don't want to make the pledges involved or abide by the code's rules.
So if you can make a choice between a garage that has singed up and one that hasn't, we'd urge you to go for a member.
The more motorists do that, the more garages will feel the pressure to join the scheme and buck their ideas up.
If you do use a member of the code, fill in the satisfaction survey that should be readily available at the garages.
Giving the SMMT and RMIF as much information as possible on where garages are going right, and wrong, will help everyone improve the service on offer.