Decided, as the weather was excellent for crawling under cars, to change out the crank sensor anyway.
Aided by Mark's previously posted pictures the connector was easy to spot and disconnected by pushing the wire retainer in toward the plug. The intercooler to inlet manifold was also removed for clearance.
Finding the sensor was impossible from above due to its location so front of the car was jacked up on the passenger side and the wheel removed with the plan being to drop the under tray for access. On getting the wheel off the sensor can be seen through the gap between the wishbone and the inner wing. Now comes the assessment section, if your arms are thin and long enough the job can be done without dropping the tray but it is tight and awkward even with long thin arms.
Tooling wise an E8 star socket with about 3 long 1/4" drive extensions and a ratchet to remove the sensor bolt, small cutters to remove the two tie wraps on the cable between the connector and the sensor and a 7mm socket + driver for the hose clips.
Once the sensor is removed check the "O" ring has come out as well, remove any debris from around the hole and fit the new sensor making sure it goes in square and fully, you'll feel the "O" ring slide home.
Re-route the cable and secure with tie wraps, much easier said than done but patience prevails, top hose back on, wheel on and away you go.
I have no idea if it has done any good as the temperatures have been fairly high, for November, but so far it has been okay down to 4 degrees C.
To minimise the changes for fault finding I have re-fitted the chip and fitted a new teperature sensor at the thermostat.
I'll update if anything comes to light over the next few weeks.