The IAM retest scheme is their ‘IAM Fellow’ thing:
Similar to RoSPA, you’ll need to retest every 3 years, and the membership is £49 a year to cover that retest cost.
Been discussed in our group a bit, but been little take up or interest in it from our membership, I suspect due to extra cost and effort required by members. Our impression is that it’s an offering more suited for someone riding commercially where the maintenance of skills is crucial, or something employers wish to verify. TBH Blood Biking could be considered to fit this, but it’s perhaps not something for someone just riding socially.
The other interesting new-ish IAM offering is their Masters scheme. A much higher level grade, highest civilian motoring/riding qualification in the UK from what I understand.