Van is fixed. The fault was the loom trapped between the roof frame and the surround of the pop up roof, rubbing against the frame at the rear left side. It may be that the T6.1 looms are thicker so was a genuine error. All fixed and protected, thanks for all the help which helped me narrow it down to within an inch of the damage. The converter found it in about 10 mins from my checks and all the forums help.