After numerous footerings and head scratching we wired so that the wiper switches on and off but without the intermittant and autostop function.
Haynes very kindly does not show a wiring schematic for the the rear wiper circuit, (doesn't show any avant specific diags.) so we weren't entirely sure of how the circuit works with the relay etc and the small PCB in the wiper unit.
I'm part wondering if it's down to the wiper unit being from an Octavia estate, even though it looks identicle the circuitrt may be slightly different. Anyhoo, I'm now chuffed. Not had a working rear wiper since buying stinky. Skoosher just dribbles down the inside of the rear lid but that's a fix for another day. Just not going to use it til then.