Gap Insurance - nicnac
Is gap insurance a good idea on cars bought on HP. Also where can i buy it. Can i buy it yearly or do i have to get for the whole term on the hp contract.
Gap Insurance - Xileno {P}
I would say essential if you're buying on HP. Otherwise if your car was written off, you could end up still paying out your monthly premiums for the full capital borrowed but have no car and probably only market value from the insurance company as pay out.

Don't know about your other questions.
Gap Insurance - PR {P}
Do a google search, plenty on there. I got mine from a website I found. Undercut the dealer by a good £150.
Gap Insurance - IanJohnson
After the wife's A2 was written off at less than 2 years old I regard it as essential.

There are different types - you can buy cover for loan/ HP or to the invoice value of the new car (or book value of an older car) but AFAIK you have to buy or the whole period up front. If you buy a year's cover then the second year will be based on the value of the car at the start of the second year (not new price)

Not painfull since we have just bought 3 years cover on line for a new car with claim limit of £15k for £200 (underwritten by Hitachi).

Half the price the Audi dealer billed us for similar cover 2 years ago - but looking back that was still a good deal!