I would have thought you would be claiming on the house insurance for the keys.
Thanks for the advice - I might have dealt with this entirely myself if I had a bit more time to spare but there is a lot of other stuff to sort out after the break-in.
The house insurance has a specific exclusion for car keys - they are considered as a "car accessory". This seems to be quite normal; our car insurance company didn't query it at all and are dealing with the issue. Of course, this means that I have had to pay two excesses!