When I bought my Clio last year I foolishly didn’t test the windscreen washers, only noticing that they didn’t work on the drive home.
I spent some time diagnosing the problem. Eventually I unclipped the valve from the pump mechanism and dismantled it (it unclips apart). There is a rubber cylinder inside that was swollen at the ends (presumably previous owner added radiator coolant into the washer bottle!), I used some emery paper to sand the rubber back into shape and when I reassembled the pump it worked perfectly, yay.
Just thought I'd post this in-case anybody else had the same problem.