Thanks for the info Joey.
I will be out at the weekend with my tape measure. I assume they are correct as I would have thought the blades would not be parallel to the bottom of the window if they were out.
I have checked for play and all seems good. I just hoped there may have been a new bush or bracket that could eliminate juddering completely.
I guess that I have to be methodical about changing wipers regularly. I usually use the genuine VX ones from Autovaux (as they are only a couple of miles up the road from me). Are there any better brands to use?
Paul