Hi,
Sorry to hear about the trouble you are experiencing. Not sure I can help much but will, hopefully, add a little to what you have already been told.
Barneyrubble mentioned the accidental damage cover with the Nikon insurance. I have it also and am used to interpreting insurance wordings (used to write them). My reading of this is that the damage caused to the camera is excluded as it was caused by an item introduced to the camera, viz. the CF card.
The wording is "Electrical and/or mechanical breakdown if caused by.....the fitting of any accessory to the product".
This assumes the card is the faulty item.
All is not lost, however. You purchased the card from Jessops and they carry the responsibility as the item was "not fit for purpose" and it has caused subsequent damage to the camera..
I suggest you look at this link:
http://www.berr.gov.uk/whatwedo/consumers/fact-sheets/page38311.html
I think it may help your case if you appear knowledgable about your rights. The warranties and insurance are not key here, but your rights under The Sale of Goods Act are.
Having said that a mixture of standing strongly for your rights and a few tears will melt most men.
Good luck.
Ken