Two manhole covers, from different times:
This cover is in the road outside 10 Grosvenor Road.
It’s 14 inches / 35cm diameter and must have been fitted between 1874 and 1894 when Brentford Local Board was in existence.
The one labelled manhole is in Albany Road outside the gate of St Paul’s Rec.
It’s about 18 inches / 46cm diameter and must have been fitted some time between 1894 and the 1920s when the Urban District Council was in existence.
There may well be other historic manhole covers to be found.