On 26/01/2019 17:35, GB wrote:
I needed to buy a Yale 89 night latch in a hurry, to replace a broken
one. The only one available was one with a deadlocking facility. This is
the only exit from a flat, so it's possible somebody could get locked
in. Does anyone know if it's possible to disable the deadlock on one of
these?

If it is the only exit, then it is the only way in. You can only
deadlock it from the outside. But would a person leaving someone inside
normally deadlock it? Theoretically possible, not much risk if sensibly
managed. I suppose for a couple where one has dementia and is paranoid
about locking up, it might not be a good idea.