We went for a walk down most of the Wigan locks on the Leeds-Liverpool Canal on Boxing Day. I'd not checked for locations of benchmarks beforehand & spotted precisely zero! Looking at the 1894 OS 25 inch map afterwards I counted 19 marks that we walked past the location of. Some will have disappeared - bridges widened, buildings demolished, etc. - but I thought I would have found at least one.
On Friday we took the grandchildren to see the (not as famous as I think it should be ) Meccano Bridge at the head of Prestolee Locks on the old Manchester, Bolton & Bury Canal. Here I spotted one in the wall as we walked down next to the flight of locks. I've not found it marked on any maps I've looked at but it is in the OS database linked to earlier.
Manchester Bolton & Bury Canal Society have a similar photo, but taken from the other side of the channel showing the original bridge
(From MB&BCS Key Facts page)
Commuting, Day rides, Audax, Incidents, etc.