Hi all,
Been seeing this as a recurrent issue.
I had the problem - changing the battery means the radio gets reset.
All you need to do, is to approach your local UK Honda dealer and ask very nicely.
I bought my car from CarGiant, so not from Honda dealer, and yet just being very polite and courteous to the staff granted me a 5-digit code that works for my S/N. Take a screenshot of the Serial Number, be nice, and they'll help.
Apparently only afew staff have access to the system, and apparently can take some time to load up and connect to the central servers. So you will need to be patient and perhaps return another day. I had to. But I got it for free.
Hope that helps others.