In a shop it is health and safety at work act not Part P so all you need is insurance and knowledge there is no need to be a scheme member.
If it is considered as a domestic then it depends where you live. Wales still has kitchens on the list but England does not. Not a clue about Scotland.
If it did need notifying the cost is silly just not worth doing. It's starts with first £2000 worth of work and if your doing £2000 worth it's not a bad price but for £200 worth cost as much to notify as do the work.
I would from what you say think all you need to do is issue the minor works certificate.
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