Bose: "Contacting the examiners may be one way but it one hell of an exercise to reconcile the examiners records with the CAA records and one could ask if there is motivation on the part of the CAA to that sort of exercise."
Why would you or the CAA need to do any reconciliation? It would be a very simple matter for either the CAA or AOPA to contact the relatively small number (guess: around 150?) of FEs and get accurate info about IMC tests; a voluntary survey will take longer and is unlikely to produce accurate data.
Presumably all you need to know is the date and CAA reference number for all IMC tests performed over the last 2-3 years.
The only thing an FE survey wouldn't catch are the people using UK CPL privileges, but your proposed survey is unlikely to catch them either.
HFD
A possible solution but still only going to give me renewed numbers which is not much use in isolation.
DFC makes sense over the long term of logging more data during the renewal but that means it will take me at least 2 years to get any data to work with that is representative. Good for the long term as it would allow me to cross check what we gather now.
What I am looking for are those numbers and the actual usage of the IMCR, hours flown etc. We could have a thousand pilots who are renewed but only ever use the rating at renewal. This will skew the results. To build a genuine safety case I want to be able to say for example that there are 2000 IMC holders who are currently renewed, of this number x% use it for xhrs per year flying x number of approaches. The primary uses of the IMCr are x. Tied with the safety record this would provide compelling proof that the rating gives clear benefits to UK flyers. This data could then be compared to data collected as suggested by DFC and give us a quality check.