I gave up in the end, it was either the skreem unit or the bcm. I didn't investigate any further as both exceeded the money I wanted to spend on the car.

They key was sending the signal it just wasn't being received by the car. The pump in the boot was fine as every worked from the dash switch which I confirmed by visual inspection. The skreem has to be a codes one using your vin number. And there were mixed opinions as to if the bcm needed to be a vin match or just the exact part number.

Hope this helps, good luck. If you do ifnd out what it was please update the thread to help future owners