just looked into this a bit more for you and a cat c write off is described as:
"described as major damage (eg kinked roof), such vehicles can be repaired by a qualified repairer using a jig, specialist tools and full workshop facilities"
so looking at the pictures i cannot understand why they are classing it as a cat c. Most of our underwriters will actually require an engineers report when insuring a category C write off stating that the vehicle has been repaired to a good standard and is safe to use on the road. From the damage pictured i would expect it to be a Cat D write off which is described as:
"best described as DIY repair, vehicles in this category only require external panels. The chassis, front crossmembers and steering are all unaffected"
Sounds more like it to me, we would insure a cat D with just a copy of the V5 and MOT certs.
Hope this information is usefull/makes sense, keep me posted how you get on....

Martin