Three decent sized images in this this blog post. On the course of Potters Bar Golf Club - closed in 2018.
(A director fringe golf club closing! This forum thread makes one suggestion: “For a long time it was a Jewish-only course . It probably left it too late to try and change.”)

The Queen's Head public house (now apparently closed) stands 50 yards to the east of this post on the corner of Coursers Road and High Street, London Colney. The entry at Historic England for the pub says “canted front bay said to have been used for the collection of Coal Tax”.

TL 175 032 Shenley Lane, London Colney South side of Broad Colney Bridge

Harper Lane, Shenley Midway between these two Tax Posts. Just a post to announce that this is No. 100 but nice echoes of Tax Posts.
Cab drivers on night shift wish that all houses showed their numbers as clearly as this.

The house where W. S. Gilbert lived and died. (Cannot think of any connection with Coal Tax Posts!)

TQ 131 926, E side of Oxhey Lane, outside No 1 "The Hollies" and immediately NW of Burntoak Farm

TQ 091 920 maps
o/s NW i/s NW   o/s NE i/s NE
i/s SW o/s SW   i/s SE o/s SE

I cannot now recall where exactly I took this photo but I am pretty sure it is just the opposite side of the path from Obelisk 52. The railway at this point is the Metropolitan Line between Northwood and Moor Park. I cannot see why London County Council Tramways should need this box - more than an hundred yards from the nearest tram tracks.

I walked about 200m either side of TQ 084 923 and saw nothing

Gates to Moor Park Mansion at TQ 078 925

Moor Park Mansion itself, TQ 074 932

The seam in the road surface indicates that this is still a boundary - between Hillingdon on the left and Three Rivers district of Hertfordshire. TQ 078 923

TQ 069 915 at the junction of White Hill and Jackets Lane. Nothing seen

++++ when the above is properly organised, use this with proper GPS derived co-ords