Due to 1/3 off selected cookware these come up for £12.33 for a pack of 6 which according to a little bit of investigation is quite a good price at £2.05 per cartridge.
Brita Maxtra Water Filter Cartridge 6 Pack are also coming up at £14.66 but I don't know if this is a good price, so £2.44 each.
Free if collected in store or if you can add it to another order.
Generally 3% cashback as well.
First post so please be kind if this is all wrong :-))