Transatlantic, if it helps, my own experience of importing goods from both the UK and from the US into Switzerland is broadly similar to those stated above.
I'm not up to date on UK rules, but I doubt (NOT sure) that you will pay import duty on an item costing only USD 40 - it depends on the value, and the customs duty category that the item falls into (a complicated numerical code which is international BTW). So probably no import duty but I'm 99% certain that you WILL pay VAT. The difference for you is that Swiss VAT is 8%, UK is, I think, 20% these days!
Further, here, and I think it's the same in UK, you pay VAT not only on the value of the goods themselves, but also on the bottom line Invoice value - i.e. INCLUDING the shipping/postage/courier charges.
If the parcel weighs less than 2 Kg then there may be an option to get the shipper to use US Post/Royal Mail rather than a courier like UPS, FedEx, etc. Axminster are very good about doing this for me for example.
The reason I ask Axi to do that is that here, (not sure about UK) the Swiss PO charge a reduced VAT on their shipping charge, and is there NO service charge. The postie just knocks at the door and you sign, pay cash (only cash) and get your parcel.
OTOH, if the vendor is using a courier such as FedEx, UPS, etc, then full VAT is charged on the shipping cost, AND there is a "service fee" as well (which is also subject to added VAT - "of course" - the bloomin' Government must get their pound of flesh!!!!).
So when the courier knocks, you have to pay both the VAT and the service charge, plus the import duty if applicable, although here anyway, you just sign for the parcel and the courier sends you an Invoice afterwards.
Detail differences between Switzerland and UK for sure, but the same principles apply I'm sure.
For a tool costing "only" 40 USD I THINK that the above add-on charges would hardly make it worth while, so it will come down to do you really want/need that tool, and is it available elsewhere? if yes (and no!), one way around the problem is to add other wanted/needed items to your order from that vendor, but there of course, you will soon run into the above 2 Kg weight limit, which here anyway, has the disadvantage of involving a courier which, as above, adds "unnecessary" charges to your overall cost.
HTH
AES