Well just to give closure, I've just returned from having the car fixed. Turned out to be the N/S ABS ring which is the original factory fitted part - so 22 years and 166K before needing replacement.
Here's the offending article. Split and corroded !
Granted the cost of one OEM ring was more than the two aftermarket parts @ £47.80 + VAT but I would much rather have a one time fix rather than have to go back in a couple of months and have to pay twice. In fact the IVS garage now won't fit aftermarket parts as it's given them so much grief.
Part of the labour included checking the codes for faults and nothing was shown for the ABS so nothing wrong with the module or sensors. I explained that the faults have never been read / cleared since I got the car in 2007 so the two that were shown for the siren battery fault (which I know is an issue) and heater fan (the blower was replaced a few months back) were cleared.
So job done and confidence restored
