Brian - Diesel has been approved in europeshire for the 172 since I've been flying/spannering on them, about the last 2 years. All info in the POH.
These service bulletins also:
172
http://www.tae-service.de/doc-downlo...Rev_0_Fuel.pdf
pa28
http://www.tae-service.de/doc-downlo...200%20Fuel.pdf