Distance selling thresholds as below.
As others have stated the distance selling thresholds are high enough that they are unlikely to be met in the first year of selling unless you are a high SKU and volume seller from the start. What will trigger VAT registration requirements in other countries, not only by the respective countries’ agencies but more quickly by the Amazon Bots, is enabling your inventory to be stored in other countries other than the UK (in your case). Make sure in your Cross-Border Fulfilment Settings under your FBA Settings that the UK is the only country identified in the Allow inventory to be stored in other countries section.
Tell the customer you only sell in uk
Most of My FBA sales are to Germany and France
I only ever have issues if i send electrical goods in where I either supply with adaptors or close the listing in that Market place
Home page > top right (Settings) > shipping settings > scroll down click EDIT > remove all regions you lon longer wish to deliver to.