I wonder if anyone has any more advice? Problem is certainly between the steering wheel and the the relay (under the metal plate near the battery) as if I bypass that with test lead the whole circuit works.

The steering wheel switch receives a single wire to its centre. This wire disappears into the steering shaft, but where it goes from there i can not tell. Also the wheel itself appears to provide the earth, so maybe its not brushing correctly to the chassis? I'm really not sure.

Anyway, managed to pass the roadworthy check so its not too drastic