The FRTOL was issued on an assessment for a few years, but it was found that RTF standards were getting bad, so the CAA decided to go back to having a separate test, as they had previously done. Microlight pilots were the exception during the 'assessment' period; they've always had to take a separate test, hence their standard of RTF has always been better! (Only joking!) It seems strange that the SPL covers you while training (you operate the radio on your instructors licence), but as soon as you get your licence, you MUST pass the exam to use the radio, but them's the rules.