jtq4u wrote:

OK providing feedback on this one in case anyone else hits the issue.
How to test for this:
Start the car and rev at 2500 revs until the temperature reaches 95 degrees in the coolant (measured via obd). Confirm the car is in a state of poor performance. Now measure the voltage across the temperature sensor. if it is around the 0.7v mark (and about 400 - 500 ohmns) then you have an over temperature situation. You can IR temperature scan the filter too if you have one of these bits of kit. When in fault condition you can further prove it to be over temperature by *(temporarily just for the test** replacing the temperature sensor with a 2k resistor. Suddenly the car will be fine again. Test very briefly to avoid permanent engine damage.

As I say the fix is a new fuel filter.