Argue all you like that it was Amazon at fault for not telling you your legal obligations, but it takes no more than 30 seconds to go to seller central help files and access this, which clearly shows that you will incur VAT obligations when you use Pan EU…
Pan-European FBA Programme Policy
The Pan-European FBA Programme (“Pan-European FBA”) allows you to fulfil offers on Amazon.co.uk, Amazon.de, Amazon.fr, Amazon.es and Amazon.it for enrolled ASINs from one inventory pool without incurring Fulfilment Fees for the European Fulfilment Network. For more information, see Pan-Europe FBA: How it Works. Your participation in Pan-European FBA is subject to this programme policy, the terms of the Amazon Services Europe Business Solutions Agreement, including Amazon’s International Seller Rules and Amazon’s programme policies. While you participate in Pan-European FBA your Multi-Country Inventory settings are enabled for the UK, France, Italy, Spain, Germany, Poland and the Czech Republic. For more information, see Multi-Country Inventory.
Placement and Storage of your FBA Inventory
By enabling Pan-European FBA, you authorise Amazon to allocate and store any of your FBA inventory in the UK, France, Germany, Italy, Spain, Poland and the Czech Republic .
Important: Storing products in an additional country to your home marketplace country will trigger additional VAT registration and reporting obligations for your business (as well as other reporting requirements such as Intrastat). You will be responsible for the collection and payment of your taxes together with the filing of all relevant returns and issuing VAT invoices/credit notes where required. To learn more about VAT see Europe Tax and Regulatory Considerations or get more information regarding External Tax Advisers here: https://services.amazon.com/solution-providers/#/search/UK/tax (English- and Chinese-language only). Please note that we will share information about your transactions and units where obligated, for example if justifiably requested by governmental entities or regulatory authorities that have jurisdiction over Amazon.