You may run into a problem if you want to change your "State of Licence Issue" from germany to the UK:
How to obtain a UK EASA Licence if you hold a non-UK medical certificate/licence | Medical | Personal Licences and Training
Read the section "PLEASE NOTE".
Try to contact the LBA (or the appropriate "Landesluftfahrtbehörde" that issued your licence) and ask under which conditions they can surrender the medical information to the CAA.
Or just get a new medical in the UK (don't know if that would work - ask the CAA: +44 1293 573700).