If the LPG install had an LPGA certificate, then I would be calling the insurance.
I'm concerned I may open a can of worms getting insurance assessors looking at the car, given that the car has not been for certification yet!!
Hmm.
My feeling is, if you get two local body shops to give you a quote, send them to the insurer and tell them you want them to do the work they probably aren't going to ask any further questions if it is just a case of fitting a new bumper.
There's always the possibility that they will dig, though.
They're aware it has LPG? Repairer may alert the insurer to its' presence but nothing more, IMHO. In which case it's a real shame you lost the certificate when your house in Gloucestershire got flooded
Kevin