Hello I do not think you can just convert a UK CPL to an EASA Part FCL licence. I had a UK CPL and converted it to a JAR one, based on some further exams I took. I did this because CAA told me with my UK CPL I could only teach on annex 2 ac. You will be able to retain the IMC on your uk licence. The rule I remember is JAR to EASA no prob UK to EASA not possible. There are more knowledgeable people than I on here tho.