Myself and Adam Lotun were both researching this .
From our findings:
Greater Manchester Police said : Unauthorised Blue Badge Parking users were still insured, but breaking traffic regulations.
More interestingly Adam had response that indicated If you use a blue badge bay unintitled your insurance wont pay for any third party damage to your car you have to seek it from the third party it seems..which was the direction of both of our enquiries... but....
"Answer: If the car was damaged by a Third Party when parked in a disabled parking bay, with or without displaying a blue badge, then the responsibility and liability still remains with the Third Party. The parking issue would be a matter for the local council."
So there is no difference in insurance with or without badge.
Thanks to Fish Insurance, GMP (via twitter) , and Disabledmotoring.org