As you know, you need to do the 14 ATPL exams. Once you've got over that mountain the flying isn't so bad.
CPL conversion training prior to test is simply "as required". 200hrs total time and a 300nm cross-country are prerequisites, but you're probably fine in those respects.
IR conversion requires 15 hours training prior to test.
Spain and the UK are both JAA states, so you get a JAA CPL/IR (fATPL) whichever way you do it.