Only a Freesat box can receive Freesat!
Sky boxes cannot receive Freesat, as Sky boxes use Sky software, and Freesat boxes use Freesat software!
A Sky box with no viewing card is basically a "free to air" box, and will receive the same "free to air" channels that a Freesat box can (either in Freesat or nonfreesat mode).
Free to air channels are those that are broadcast in the clear, with no encryption, and so do not require a viewing card or subscription. Channels like BBC1,2,3,4,itv1,2,3,4,c4,e4,m4,film , five are all free to air.
Free to view channels are those that are broadcast with encryption, and so do require a Sky viewing card, but no subscription. Current free to view channels include FiveHD< Sony tV, Pick TV and Motors TV.
Freeview is a terrestrial broadcast system, that used lands based masts to transmitt, and a TV aerial.
Freesat and Sky are extra terrestrial ssystems and require a satellite dish.
So yes a british sky box will work in spain, if conncted to a dish. It will not get Freeview.