So this is where I have got with all this this week (all information pertinent to helicopters only)....
CAA say that the option to fly CDFA or non-CDFA "rests with operators, assuming the approach designer does not prohibit non-CDFA."
Having spoken to the approach designer (NATS) PANS-OPS does not prohibit or allow CDFA or non-CDFA approaches as it is an operator’s consideration, not an approach design consideration. There aren't separate design criteria/rules that are applied if an approach is going to be CDFA or non-CDFA, the approach designer simply applies the PANS-OPS rules to provide the minimum obstacle clearance etc. So, provided you fly the approach above the step heights and minima then you are safe.
Take the NATS plate for NDB 27 Norwich as an example
http://www.ead.eurocontrol.int/eadba...2011-06-30.pdf It makes no mention of CDFA (the charts our operators provide give separate CDFA and non-CDFA minima for this procedure) which backs up the approach designers claims that it isn't a design consideration. In my honest opinion (and I am most definitely NOT an authority on this) we can therefore chose to use either technique and just obey the step heights and minima on the plate.
The CAA appreciate that we could do with some info/guidance and are trying to arrange the publication of a CAA Information Notice to help get the message out. Not sure if it will have the information from the approach designer though as that was my own leg work. Finger crossed that has helped someone!?