what is the shortest mountain in United kingdom?

https://en.wikipedia.org/wiki/Mountain says:
"In the United Kingdom and the Irish Republic, a mountain is usually defined as any summit at least 2,000 feet (or 610 metres) high, whilst the official United Kingdom government's definition of a mountain, for the purposes of access, is a summit of 600 metres or higher. In addition, some definitions also include a topographical prominence requirement, typically 100 or 500 feet (30 or 152 m)."

Looking around at https://en.wikipedia.org/wiki/List_of_mountains_of_the_British_Isles_by_relative_height I see that Beinn Mhòr is 620 m and could be said to be the shortest. https://en.wikipedia.org/wiki/Beinn_Mh%C3%B2r_%28South_Uist%29

If one goes by relative height, then it's Moel Siabod at exactly 600 m.
https://en.wikipedia.org/wiki/Moel_Siabod