Do you have all the relevant documentation for UK regulations, eg HACCP etc? Have you been approved for sales of food products in the UK market?
Remember that UK is no longer part of the EU so just having EU safety/approval documents and being approved for food sales in the EU is sadly not enough.
There is no clarification as to what import / export restrictions there could be.
I understand that all food items and supplements need to be properly labeled with translated ingredients lists etc. But the error note says that the ASIN is restricted, there is no mention of any documentation for submission.
If it is not your own brand, then the brand owner may have asked Amazon to prevent sales in the UK. Maybe they have exclusivity arrangements with another seller?