Been away for a while but now back on this problem vehicle. Today I have checked all of the above suggestions to no avail. I have fitted another knock sensor to the loom but not bolted to the engine, scoped under acceleration to check that no signal is being induced into the circuit & we still get 15 degrees retard on live data on all cylinders which leads me to belive that the ECU must look at another condition to give knock control. I also have had the chance to check another vehicle running MS70 & the lambda sensor on this also switches back to front so that was a bit of a red herring. Any further suggestions most welcome.