Clue: Spain claiming penny in tax upset economic migrant (5)
Answer: EXPAT
Explanation: Definition: economic migrant
 E(International Vehicle Registration code for Spanish-registered vehicles) **plus**(claiming) [ P(abbrev. for "penny", unit of English currency) **contained in**(in) **reversal of**(… upset, in a down clue) TAX].
Defn: An example of which is an "economic migrant", one who resides outside his/her native country to work in another country.