Martyn I am going to do the same trace for you (fingers crossed) this weekend. Its a shame your not closer because my catbypass pipes lambda sensor was removed because the pipe was polished, and currently I have the cat fitted for MOT (which has its own lambda sensor) so its just sitting there not doing anything. Once I have my trace you should be able to compair, and give you a definitive answer. One thing I know is Bad AFR, does not 100% mean lambda sensor. It just means the ECU can't keep the Air Fuel Ratio in check within given parameters, this could be because the signal coming from the lambda sensor is wrong, and thereore the ECU is not seeing the AFR correctly. That said the signal coming from the lambda sensor looks wrong to me, I would expect some variation in the voltage, and from (my bad) memory mine drifts around 0.98v to 1.01v.