When I purchase kit from the states the price includes landed shipping costs
any vat or duty applicable is paid in the UK prior to arriving at my address in
That is a slightly different scenario though. The likes of UPS and FedEx have their own customs clearing houses. If the seller has already taken any payments for duties or vat, they pass them on to HMRC. If the sender hasn't included them, UPS will demand payment before they physically hand you the goods.
Our American suppliers had already encountered problems trying to send things in to the EU. They sold on a collect from their factory and sort out your own paperwork and shipping basis. We paid the import duties (8%) and VAT as soon as the goods arrived in the UK at the HMRC clearing house.
Sending, for example, a pallet load of drill bits is relatively simple. You go to the HMRC website and use the commodity code "tree" to work out what the relevant duty is. When looking at food stuffs, if it has sugar or dairy ingredients, it is subject to tariff quotas. On Jan 1st, the EU says that, for example, two hundred tonnes of that product are allowed to enter the EU at a 8% rate per tonne, once that 200t limit is reached it becomes 8% of the value of the consignment. Buyers have no idea when the quota is going to expire, so the big boys front load their annual orders.
Going slightly off tangent, but trying to prove a disjointed point about VAT. I am self employed but no longer VAT registered. If I imported a pair of safety boots from abroad, I have to pay 20% VAT when they enter the UK even though they are VAT rated at zero to end users. Given that I am not VAT registered, I cannot claim the VAT back.