Many thanks for all your comments and advice.
Yes you were quite correct the washer jets are relatively easy to get of. I used a flat blade screwdriver and prised it off.
I was unable to clear the washer so bought a new one from my local Toyota dealer, Jemca. It was a bit expensive considering it is a small piece of plastic.
It cost me £15.92 but I guess it was not too far off the mark if I had bought it off the Internet when postage and packaging is added.
For information the part number is 85381-20280
Out of interest the guy at Jemca advised that in 90% of case where one washer jet is working then the culprit is usually the valve that feeds both jets.