When in the EU, VAT was still payable on the goods when sold to the consumer (sales between EU registered businesses were usually VAT exempt) and it was typically collected locally and passed (or perhaps more accurately credited) to the country of destination at their VAT rate for the product., so post-brexit, the seller should have reduced the coat in price to reflect the fact that they were no longer responsible for collecting the VAT. The rest of the premium is presumably made of admin and brokerage fees which again were always there, but for consumers they were usually hidden within the total shipping cost - it now seems that the couriers have decided to show these as an additional charge.
Of course, what isn't stated in the article is what the coat would have sold for in December, so we don't know whether the coat cost less than it would have done a week earlier or whether the price has remained constant, in which case they probably didn't realise that they no longer needed to include the VAT in their sales price to a UK customer. If they did know but have decided to charge the same price anyway, that is a bit "naughty".......
Mind you, I don't have a lot of sympathy for anyone that can spend £200+ on a coat, but that's for another thread.......