So just to clarify, as I wanted to put three heads on the rear of my car, I was only supplied with two extensions, so the installer got another extension from his car, but we didn't need it.

As mine is a small hatchback, they only needed one of the 2.5m extensions that was supplied with the ALP.

Hence I have two extensions spare ;

1 bag labelled 'Extension Cable for AL Sensor length 2.5m'
1 bag labelled 'Extension Cable for AL G9 RX Sensor length 2.5m'

I take it from the findings then, that I shouldn't use the AL G9 RX extension with the ALP, or it might actually be OK if the pin assignments aren't crossed over from one end to the other ? (I'll check the pin outs tomorrow with a multi meter)