I’m in the USA. I just bumped into this today, either because it was my first sale to the UK this year, or because I got un update to my Endicia software. The Endicia software pointed me at a FAQ https://endicia.custhelp.com/app/answers/detail/a_id/7318 which, amongst other things, says
" Do Sellers on eBay, Amazon or another Online Marketplace have to Collect VAT?
Very simply, yes. Online marketplaces (OMP) such as eBay, Amazon, Etsy and others will be responsible for collecting the VAT from the buyer when the sale occurs on their website as long as the price is £135 or less. For sales that are over £135, the OMP will not collect the VAT and existing import rules will go into effect (seller pays at port of entry)."
Which seems backwards to me i.e. all the little guys have to do more paperwork, but big sellers don’t. However it removes the penny-ha’penny charges and busywork for UK customs, so it makes sense in those terms.
I already rely on Endicia to automatically print out the required copies for each country, and they seem to be on the ball.
So for the time being I’m going to continue the same policy as I do for all countries - keep shipping to them till something breaks. If it breaks, cut them off and don’t ship there anymore. However the UK is maybe 20% of my sales, so maybe I give them a defined shipping rate (more markup than other places due to the hassle) and a note that I’ll be sending the customer an invoice for 20% to cover the VAT with an explanation that this is because the idiots in Westminster that they elected are doing this to them, not me, and they should write to their MP, and no other country in the world does this. In the meantime they have 7 days to pay up or I cancel their order and refund.