Rubber insulation has a 25 year lifespan. It hasn't been used for over 50 years...
There is no earth connection, and the backboxes are metal. If one of those wires contacts the metal box, it will be live, including the screws securing the lightswitch.
Fuses will not blow, but anyone touching the exposed metal parts will get an electric shock.
This of course does nothing, as just moving the wire causes more insulation to fall off.
The only slightly good thing is this switch has a plastic box - but this switch is far more recent that the wiring connected to it.
This mess dates from the 1940s or early 1950s and should have been replaced decades ago. Prior to these photographs being taken in 2010, all of it was still in use.
It was pure luck which prevented serious injury, death or fire.