Economy shipping from the UK will generally be either ParcelForce (which often still gets held up in customs, even if you don't have to pay any customs) or Royal Mail. Vendors like Scotweb, however prefer to ship with more solid shippers with tracking and insurance, especially if they sare sending something expensive overseas---for their own security as well as yours. So even if you choose economy shipping, they may still decide to ship with whomever they choose, at their expense.