This cylinder rim nightlatch came off an outer London tower block of flats, built I guess c1960, in 1969, after a wave of burglaries in the block.
There is no deadlocking function, and no marking on the latch. The aluminium cylinder was marked ‘Sidleen’. The pull-up linterior latch handle, and snib, appeared to be a ‘wannabe’ Ingersol SC71 rimlatch. I have never seen another like it.
And neither had anyone else who saw it on the Lock Collectors’ stand at several trade shows. Without considering of much interest, but it was small and easily accessible at home, I took it to a Lockex, together with a couple of Ingersol Impregnable cylinders. I was surprised at the interest in them.
Later, Andrew Taylor (Jack Taylor’s son) told me that his father had briefly worked at Sidleen, and my rimlatch seemed to be a short test run for the latch handle and snib that would later be used on the Ingersol rimlatch.
I had previously only known Sidleen for the tubular lock (9 or 10 pin, I forget which) fitted to parking meters
https://collection.sciencemuseumgroup.org.uk/objects/co50504/two-dgi-sidleen-locks-and-keys
http://www.historywebsite.co.uk/Museum/locks/gazetteer/gazs.htm
became Sidlock. They do not appear to be still trading.
Pictures to follow.