I don't think you can cross over the ground exams or your medical to the spanish system
If you have a UK Medical and UK exam passes you have to do the UK CPL course after you have been issued that you can add the IR rating in any JAR state in theory. Thier has been a slight change with the Irish CAA on this but thats about it.
I wouldn't bother looking to save money going abroad for this stage in your training. If you want to work in spain do the spanish course if you want to work in the UK do your training in the UK and Jerez i am counting as UK . By having a spanish license your just giving them another excuse to chuck your CV in the bucket.