I'm assuming you're marketing this in the UK?
If so, there is no formal regulatory definition of "natural" (other than certain specific cases e,g, natural flavourings and natural mineral waters), so your general obligation would be the "Fair Information Practices" required under Article 7 of Regulation (EU) 1169/2011.
Nonetheless the FSA has published some guidance on their interpretation/expectation around the use of terms such as "fresh", "pure", "natural" etc - it's now ancient, having not been updated since 2008(!), but I've attached a copy for your reference.
The guidance does advise that compound foods shouldn't be called "natural" in their own right, which make sense in that one can't catch a pre-breaded whitebait in the wild. It does however provide for the term to be used with suitable wording in respect of the ingredients used in the composite product.
In my opinion the flour is potentially acceptable (since it's made from a natural ingredient by what is arguably a "traditional" process), but you'd need to look into the nature of the potato starch and any other additives being used.
There is acceptance that the term "natural" could be used "to describe food ingredients obtained from recognised food sources and which meet the criteria in (a)" - (a) being section 55(a) of the guidance document - such that a carefully worded version of the claim might be permissible, e.g. "100% of ingredients made from natural sources".
I'd look into what your potato starch and other components in the breading are made from (and how they're made) and if the guidance still isn't sufficiently clear (which is often the case) then have a chat with your local Trading Standards team. IMEX they're pretty helpful if people contact them proactively, and if you want "assured advice", i.e. something that carries weight that you can show in the event of any queries/challenges, then it's far far cheaper than using a specialist consultancy service whilst also theoretically carrying more significance.
Edit: Now with the attachment this time!
Edited by pHruit, 01 June 2022 - 01:57 PM.