Just discovered this yesterday when buying laundry powder and conditioner for my son whose skin has been horribly dry, verging on eczema for a couple of months now - Boots Health Club entitles you to half price on loads of their products including washing products.
Here's a list of all the half price items:
www.bootshealthclub.com/half_price_list.php
It's free to join so definitely worth doing.
Sorry if this has already been posted!