After using Canon's website ([...] to spot fake batteries, I have closely looked at this battery accessory and have found the text on the cardboard sleeve has mis-spellings and lacking some punctuation. The label around the battery is of lower quality than the original supplied with the camera. However the real tell-tail is the plastic mouldings on the battery itself which are not a match for the original camera supplied battery. One of particular note is on the opposite end from the contacts, where the original battery has a seam in its construction, yet the one sold by Gadgetstore at £29.99 has a poor indent in the moulding to 'represent' the same seam.
Yes, my cardboard sleeve does have a Canon hologram sticker on it, but I'm never sure why we should believe the hologram makes the unit official. I don't believe this one is a Canon original.