Jury's out somewhat then but people seem to like the B+W polarisers. Is this the one I'm after? Seems like a very reasonable price (even with the £27 postage)? Anyone used this firm?
http://www.bhphotovideo.com/c/product/10873-REG/B_W_65016142_105mm_Kaeseman_Circular_Polarizing.html
This filter will slot into the Lee 105mm adaptor ring presumably (to attach to the front of my foundation kit holder)?
I should have said that this for wide angle lenses (Sigma 10-20mm and Sigma 17-70) on an APC sensor (Canon 450d). So far no problems with said Sigma lenses but have only used them a couple of times each since buying a month ago.
Thanks for all the help guys.