Having watched the dash cam many times have been able to work out what happened, so stopped on steep hill in 4 wheel drive low box but no rear diff lock on, HB on transmission and held no problem, did consider stopping engine and putting in gear but battery a bit low after the heavy winching, so did not, all held well till I came back to get something and got in drivers seat and picked up a few items that had come of the dash due to the steep up hill angle got back out and shut the door (just as well or I would have lost it) but heard a click on the dash cam, can only assume this was the start of the front Lokka disengaging then a little latter when I just lent gently on the NSF wing heard another click (also on the dash cam footage) this was when it just let go, one rear wheel was only in light contact with the ground so it was the one front wheel via the Lokka that was holding it, which then let go, so basically the HB held cos of 4 wheel and the Lokka, had I engaged the rear diff lock it would not have happened, so lesson learnt, flick the rear diff lock on when HB on steep and rough ground, Rick