It's impassable in winter and the "unsuitable for motor vehicles" signs are there for good reason.
At certain times the ford at the southern end presents no problem, but the section between the two entrances to High Laver FP 29 (through the field directly to the west) is impassable. It's possible to walk on the verge, on the western side, from the south, but it disappears as you go around the bend. In the north, the lower part of the section between Leather Bottle farm and the northern entrance to High Laver FP 29 is impassable as well.
There is one escape route though - if approaching from the south, you can take the steps up to the southern entrance to High Laver FP 29 and you'll see a path hewn out of the verge of the field, running parallel to Watery Lane. From the footprints, quite obviously nobody bothers following the direct line of the footpath across the field. When you get to the northern entrance to the footpath off Watery Lane, you can either get back on the road (if it isn't too flooded) or follow the path round to the west and be brought out on High Laver Road.
In a nutshell though, unless it's summer, stay well away I'd say. There's no point going through here when there's High Laver Road and Little Laver Road running parallel either side of it.