Welll after about of head scratching it's sorted. I stripped back the wiring and couldn't see any breaks, so went ahead and changed the alternater and still it wasn't sorted.

So did all the wiring again and stripped it right back only to find a break half way along in the smart charge loom where it's clipped to the fan housing. Just shows you need to check all of it not just a bit!!

Cost me £100 for the alternater that I didn't need but oh well I cba taking it back off so it's staying on.

Thanks for the advice