I had my bi annual last year, licence signed by cfi. End of. Not informed of any form I had to complete... have I been flying illegally for 12 months??
You certainly should have filled in SRG1119
SRG1119: Type/Instrument/Class Ratings (Aeroplane), Licensing/ATPL Skill Test and Proficiency Check - Application | Publications | About the CAA
There's no fee, as far as I'm aware it's purely for notification, they scan it in and keep it on file. Probably best to investigate this with whoever signed off your licence, there's a chance they may have filled one out and sent it without you knowing.