muck-savage,
The 'rules' on licencing are here
http://www.caa.co.uk/docs/33/LASORS.PDF I am sure that you will be able to take the IR/Multi in Spain. Remember, you are adding a JAR ME rating and an IR(ME), not a Spanish ME and IR(ME). This may have been why the CAA said no
I'd give the CAA another call
