Hi Carl,
I had a problem with the Key on my s type. I had an examination a few days ago with and the issue about the performance was sorted out. Then the keys started to fail and a new battery was needed and fitted but still the car was getting lower performance notwithstanding the new battery.
I know a very small but extremely good local business so I went to their 3 man office. They felt that the Key was a failure even thought it was starting the engine just opened by hand, The leading engineer told be that there was nothing at all wrong with the engine but the key was a 100% wrong. I came away with 2 keys that were very different but vert good and the engine was as smooth as ever.
If you ever need a new key for your Jaguar look up DUPLICUT VEHICLE LOCKSMITHS [0121 354 1499] - unfortunately for you as they are in Sutton Coldfield.
Regards,
Peter.