Salter vintage post office scales

My dad had these old Post Office scales in the house for many years but following a clear out they are now sitting in his garage. Before they are moved on by my mother to the dump, it would be good to know if this is the kind of thing that is of interest to collectors. Does anyone know how old they may be and when they would no longer be in use? They probably were bought somewhere in the East Midlands or in Yorkshire.