The thanks is for all the help. Even if it doesn't go through, all the suggestions have given me somewhere to start.
Got intouch with Genuine parts. They said the sensor was a genuine one, so ordered one. Just had a email to tell me that they don't have it in stock as it is no longer available, but they can supply a aftermarket one.
you can pick up an aftermarket one from any decent motor factors to save waiting for deliveries
genuine £10 slow post clicky plenty of others on ebay too
but check live data if possible first ,your sensor may be fine
worth checking the wet stat is not stuck open (stopping the engine ever reaching running temp)
if this is the car that had a headgasket replaced
lambdas could be contaminated
again, live data would show if they where switching,reading correct voltage
and consider my earlier advice about cataclean and warming engine up and cat before retest
if you have an ohm meter/multi-meter ,you can test the temp sensor for resistance
info
here clicky topbuzz website