Just wanted to say a big thank-you to Gotlus and others for posting this info. The same problem had been bugging me for ages in my 53-reg Micra and had been beginning to getting worse. Garages told me because the problem was intermittent, and not happening when they had the car in, they couldn't diagnose the issue.
On the basis of info from this page I took the car in to get the washer pump replaced (for info: cost £27 for part, £30 for labour, plus VAT) and all now is fixed. Thanks again!
Kaplan, March 2013