Stuart, thanks for the update. First of all, I might have confused it with another car and the engine light doesn't come on when the MAF sensor is disconnected but that shouldn't bother us.
Nevertheless, it is obvious that without the MAF sensor connected, the ECU must fall back to fixed stored values. These values are richer in the mix for safety against engine damage.
The messages in the OBD2 you mentioned are totally normal when you disconnect the MAF sensor.
Did you drive again with connected MAF sensor at the end?
I would proceed as follows. My thought is that you drive another one or two times a distance of several miles - with MAF sensor connected, and without MAF sensor connected.
The error of jerky driving with the MAF sensor connected should be repeatable. Driving without MAF sensor should be repeated without this fault. Thus I would like to exclude the possibility that it was only a random result today.
If everything turns out as intended and as expected, the error could be further circled.
As I wrote, with my car the error was always there... with and without connected MAF sensor. This suggests that the fault in your car has a different origin than mine.
If the error repeatedly disappears when the MAF sensor is not connected, I would actually focus the further analysis on the MAF sensor.
Three things can perhaps play a role here.
1) the MAF sensor itself is defective and must be replaced
2) The plug is defective. I spoke to the master mechanic of my Morgan workshop about our problem when I changed the BPS switch. He told me that they couldn't find a similar defect at first, when they tested the same Sigma 4/4 as ours. The MAF sensor was replaced twice (for testing purposes only, not at the customer's expense). But nothing got better.
In the end they discovered that one of these five wires had a cold solder joint on the plug. They re-soldered the connection and the fault was gone.
I would remove this red plastic oval of the MAF sensor plug with a very fine pair of pliers and check if everything is ok behind it. It looks exactly like in your photo of the gas pedal plug. There could be a grease film behind it, which causes a light current conduction between the pins. At least rainwater and washing water goes there. Spray with contact spray and let it dry very carefully. Afterwards very carefully push the red oval plastic part back onto the free standing and vulnerable pins.
3) This is just my guess: The way to the MAF sensor is much shorter in the original Ford Fiesta or Focus. It could be, so my guess, that under the wrapping these wires are extended at MMC, soldering or cold pressed. Because with the Morgan the way to the MAF sensor is much longer. This can also be a source of error.
So first drive again to create the symptoms repeatable and to stop them repeatable.
Then test these three possibilities described above. This is only my suggestion, maybe our TM friends have other ideas.
I have the good feeling that you have come a step further. At first enjoy your GTASSABPC test, it sounds good:)
