Evidently Newcastle United Football Club is proposing to add slides to long slopes between the gates of St. James' Park and the subway station. The article notes a slide exists at a Dutch train station, where it is called a "transfer accelerator." (Actually, since it's in Dutchia, it's called a "trjansfjer aksjelerjatjor".)
These actually wouldn't be so crazy if they weren't flush with the ground. Sitting down on something seat-high and getting off something seat-high would be a better fit for commuters. If it's just designed to be a bit of whimsy, or to give kids something to do while their parents take the stairs, then an at-grade slide is fine, but if they actually want to increase the number of people using it, a slight improvement will go a long way.