This list may not be consistent with the previous list, because the total elevation gain for a segment will only be added to the database when the details of the segment are viewed
Take these with a pinch of salt, Strava contains quite a few segments with dodgy average grades. To reduce these rogue segments, I have filtered out any segments under 1km.
At time of writing, most segments in this table are in Richmond Park, London. Get searching for segments in other areas!
Mostly Regents Park in London.
If your GPS loses its mind, then turn it into a segment, grab a KOM (as the only person who'll ever complete the impossible segment) and maybe top this table.