Assuming you have done your ground school ATPL theory exams and your CPL under the CAA, then you have fulfilled all criteria to meet the license issue requirements and there should be no further problems.
Since the IR is a rating that is added on to the license, it can be done in any JAA country and has to be recognised by the CAA. It's all in JAR-OPS if you can be bothered reading it, or alternatively in the latest version of LASORS.