You can get husks in Holland & Barrat and if you pick up their Healthy Magazine there's a coupon for them at half price (they're usually 11.99 & the magazines 1.50 so worth doing) I've not read it but it looks like not a bad mag for the price, I bought LL Mag which cost 3.20 in the week and it was crap, waste of money really....
Not sure about Fibresure, but I just feel that it's unlikely to be okay with Cambridge. The psyllium husks are okay though. You can usually get the capsule form of them in health food shops. Most health food online stores have them too.
Originally I bought the pills from Holland & Barrett but to be honest they didn't work very well for me (took the 6 as recommended & still had problems). I have just bought the husks from Healthspan as recommended by Russian Doll & in comparison I think these are much better value. They also do free delivery & they only took 4 days to arrive. Also I understand that you can use these husks to make CD porridge (do a thread search for porridge & you'll find plenty of recipes).