Hi John, Not sure what mileage you do, but if you do less than 6000 miles a year, this can give you a big discount, also some banks offer special deals for their customers, see if you can get someone who knows about cars to come out with you.
You would also need to take it for a long drive when the engine is cold, check all switches, windows, lights listen for noises whilst driving, check suspension, if they have a timing belt,cam belt you will need to know when these were changed.
Basically if the interior of the car is tatty, I would say that the car has not been looked after very well, but most Jag drivers take pride in their cars, hope this helps a little bit (average mileage should be 10 -12,000 miles a year, tyres are also dear for Jags, Good luck.