I'm still chasing this overheating issue so further suggestions will be appreciated.
Reminder: MG TF 2002 135 with air. Getting near max temp (almost to the 4/4 point) in stop-start traffic, returns to normal temp quickly when moving. The engine bay fan activates when the car is hot therefor temperature sensor seems to be working.
So, as suggested, the engine fan has been checked and found to work fine when hit with 12 volts, so can now assume it is not getting a signal to turn on as coolant level rises. 
I've now found that the AC isn't working although the refrigerant level is fine and the AC guy suggests it is unlikely that the compressor is faulty, thus suspects it's not getting the appropriate signal to turn on. (The idea was to turn on the air to activate the AC fan thus cooling the radiator, at least until a solution to possible ECU fault can be found.)
Also, I have learnt that the relay sitting between the fuse box and the 70 amp fuse under the front bonnet operates the cooling fans. My question now is, does this relay also operate the AC switching? If so, could it be the relay at fault and not the ECU? Guess I'm looking/hoping for a cause other than the ECU - I've been in communication with Bitz and they don't have the appropriate ECU set as the air-conditioned models there in the UK are rare.

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