A loose screw

This little ( tiny. ) grub screw is supposed to hold the kitchen door knob to the lock spindle but keeps falling out as I am with these small things.
The one for the snug also fell out and rolled and lost down a crack in the floorboards - hence the door handles are likely to come away in ones hand. Busy day with meetings am & pm.
Dyker on the job on a sunny but chilly ( for here) day. Panic to close the gate as about to leave to prevent some loose cews entering the garden - they ran off to the main road and had gone by the time we got out.