Spurred on by this info I thought I would do a bit of research.  found this    https://taxation-customs.ec.europa.eu/guide-vat-refund-visitors-eu_en   If on a  cruise ship it's not at all clear how the process described would work, in our case theoretically I would need to find customs officers in Madeira to stamp all my receipts as that is the last port of call.  In practise it's not going to be worth the bother for the amounts involved.    But the link maybe helpf