The Ordnance Survey list has just 1 Benchmark in grid SE1548, which is a normal Cut Mark

1 – CUT MARK – BR PARA HUNDWITH BECK N SIDE LOW PARK RD
FOUND IN GOOD CONDITION
The Cut mark is on the parapet of the bridge over Hundwith Beck, on the North side of Low Park Road
This mark shows why you need the description as well as the grid reference to find these marks… the map clearly shows that it appears to be on the South side of the road whereas the description tells you where it is – on the North side…