Your spuds look amazing! I havent grown Maris piper so don't know how long they would store, but my King Edwards and PFA keep until April / May in hessian sacks in the garage. One word of caution. It's very important only to store perfect potatoes. I go through all of mine individually, putting on one side any that are damaged eg by slugs (even the tiniest hole!) or have any signs of rot or anything else not quite right. These get eaten first. They don't usually go into sacks as I want to be able to keep a close eye on them. When the perfect potatoes are in the sacks, its still a good idea to inspect them from time to time just to make sure that no rot has appeared in any of them, as it can quickly spread. I don't know how light your shed is, but I usually drape another empty sack over the sacks with potatoes, to make sure as much light is excluded as possible.
HTH
Kitty Katt