When I trained as a childminder a few years ago, it was made perfectly clear that we needed parents' permission for outings, including car journeys. The NCMA provides permission forms for this very reason.
Blonde - it may be true that legally cms can go where they want without asking the parents' permission, but it is not good practice. As for cms being just like mums - they are also supposed to be professionals who are part of early years' care and are expected to provide professional, child-centred care, not just fit the child in with their life. Besides, a sensible mum caught in this cm's situation would have avoided taking the children on a hazardous car journey, followed by a stressful and unpleasant shopping trip. As a mum in her position I would have sent my husband to cope with the shopping whilst I did things with the children. Why make them suffer too?
Mimosa - your childminder should have asked you to sign forms giving permission for outings. There are permission forms for everything and it can seem quite irritating, but it ensures both childminder and parent have an agreement and know where they stand. I think your cm had no business to take your children out in her car without gaining your permission first.
Childminders are a business, as excusemoi points out, and should behave as one. This childminder is entirely unprofessional, as far as I can see, and is just treating the job as a useful earner whilst she gets on with her day-to-day life.
Apart from the obvious problems you have stated, Mimosa, it is also clear that you and this cm have very different ideas about childcare (eg your attitudes to giving children chocolate). It would suit you better if you could find a cm who had a similar outlook to you. But I realise this is too difficult in your situation, and I'm glad that you have found a solution.
Lukymum - you are so right about there being some wonderful cms out there. My cm has a gift with children that I envy. Her first concern is always for the children and she would certainly never behave as mimosa's cm has done. My son absolutely adores her.
Mimosa - hope you can have a happy Christmas now you have made a decision. I think you have done the right thing.