Hi Guys thanks for so much for your input on this one, the job is back in Monday. Out of interest I have taken gas readings which are as follows [CO..01] [CO2 14.97] [O2 .35] [Hc 28ppm] near perfect figures there’s no problem on the control side. I have wiggled the wires and also tested with headlamp bulb back to ECU, having struggled that wretched armour casing off, ensuring no resistance in wiring. The wiring is short to the ECU and only one entry through vehicle [no chaffing]

I like Terry's suggestion of scoping the heater circuit from cold and seeing how long the O2 sensor is supplied voltage, I assume when conditions are right the heater circuit is switched off. I do also have a genuine sensor waiting to go on if required, all £164.00 worth of sensor compared to NGK £48.00. It will be interesting to compare the resistance of both sensors heater circuits. I never thought a simple heater circuit problem could cause so much hassle.
Thanks for your input I will keep you informed of data & outcome hopefully Monday.
John Kennard.