The good news: In Wilkinsons (at least, in my local Wilkinsons) all of the L/XL sizes of Drynites and Underjams are half price. That's less than £3 a pack for Drynites and around £2.50 for Underjams. I recommend you stock up if you can! I'm going back tomorrow to pick up some more before they are all gone.
The bad news: This means that they are not selling well enough, and it looks like Wilkinsons are going to take the larger sizes off the shelves after only having them a few weeks.