@Trickedem and myself did that path a couple of years back on an Audax. Surprisingly good surface for cycling.Check out cycle route maps at https://cycle.travel/map
The cycle path is actually 20m to the North of the A299, behind the trees, so it cant be seen from the road.
It crosses the road on a footbridge, it's a surprisingly good path.
Note: if you are following it from West to East then ensure you follow the signs when it suggests you go up a little path alongside the road, otherwise half a mile later you will be lifting your bike over a gate
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Cycle Path is on the left (North) side of the A299
There is a ditch, fence and trees between the path and the road, so you cant move between one and the other
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