Sorry guys, I have to disagree.
A terrestrial Freeview box probably WILL work in Spain, but only to receive the Spanish DTT transmissions.
A couple of caveats though. There have to be transmissions in your area and it has to be one of the later DTT boxes that can understand 8k transmissions as well as the 2k transmissions used in the UK.
PaulR
There's talk of the UK going over to 8k transmissions in the future. This will make the old OnDigital/ITV Digital boxes, some early Sony IDTVs and some very early Freeview redundant.