i have just been on the phone to the CAA with regards to this topic ,because there is some uncertainty as to where you should actually put the id number on your drone here is the reply to the question i asked about this from the drone and model aircraft registration scheme
they have no issue with anyone putting their operator no in the battery compartment as a back up in case the external one came off
but they say that to comply with the regs, it should be visible on the outside of the main body of the aircraft ,the reason being that if it was found then it would be able to be returned to its rightful owner ,and if a police officer wished to check the number against the data base, then he would need to be able to see it on the outside of the aircraft without having to resort to any disassembly of any kind, they said that they had had a lot of questions on this subject, so it looks like the operator id will have to be on the outside at least for now anyway
they have no issue with anyone putting their operator no in the battery compartment as a back up in case the external one came off
but they say that to comply with the regs, it should be visible on the outside of the main body of the aircraft ,the reason being that if it was found then it would be able to be returned to its rightful owner ,and if a police officer wished to check the number against the data base, then he would need to be able to see it on the outside of the aircraft without having to resort to any disassembly of any kind, they said that they had had a lot of questions on this subject, so it looks like the operator id will have to be on the outside at least for now anyway