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