rear screen washer estate

The screenwash low level light is now permanantly on, and the rear screen wash jets won't pass water(except a few dribbles on and off) sounds like an old man's prostrate problem!. The usual pipe joint in the rear loading well is not leaking, the windscreen washers and headlight washers are working. Any ideas please?

filter 

blockage 

rear washer spray 

screen washer 

Many thanks to you all, I shall try remedies on Saturday.