Wow! They took some wading through!
Thanks for the links Tim! Most of it I knew already, and indeed, only use a filter to protect the front element in adverse conditions. I quite often go to the Peak District on the gritstone, when the wind blows up there it shifts the VERY grity sand at some rate, that is one of the situations I would use one. I also shoot water, falls, mountain streams etc another situation that would call for a filter. Also I go Carping with my Son, and find the CPL a boon when trying to capture the fish in water.
I do use B&W filters on another lens, but was wondering if the Canon branded ones were on a par with them. The one I am looking at (CPL) has a RRP around £150, but is on special offer at £49!