I want to note that we (my dad is sarge_2012) have a contract with Deutsche Post/DHL for a shipping service called "Warenpost International". Which is specifically meant for small commercial items. I think the minimum number you need to do is 200/year worldwide. So it's not available to most other sellers. It comes with some restrictions to size and value and has a limit of 1kg up to which there is a price increase for each 100g.

Anyone else has to go to DHL.de and will usually use the "5kg Paket" which is the cheapest insured way to ship to the UK. That's 26.99€, but eBay does charge its fee upon that and you have to pay VAT, too, onto which eBay fees also apply. I think the seller has to calculate to pay about 33€ in total for shipping and fees. Which is of course a crazy amount.

There is a "2kg Päckchen" option, however Päckchen is not insured nor tracked and this has been the case since I was born. So this is the unsafe option in most peoples mind. However, recently they added an option for tracking and 50€ insurance. Costs a bit extra, so to the UK you'd be at 17,99€. However this is not widely known.