Atlantic or Irish ivy, Hedera hibernica. Some call it a subspecies of Hedera helix, but they have different chromosome numbers are so will not interbreed easily, therefore separate species is best.
This is the one that prefers warmer spots such as rocks and cliffs, and is less likely to be found on trees in the colder parts of the country. Last autumn I compared the two types (the other is Common Ivy or Hedera helix) and the one in the picture produces more nectar and is probably the one most folk get their autumn ivy honey from.
The leaves differ between the sterile rambling shoots and the flowering growth. This one has broader leaves of both kinds than the other species.
To be sure of the identification looking at the leaf hairs is the way to go for which you really need a microscope. Mo: the hairs have multiple branches. H. helix has them pointing all ways, pin cushion-like. H. hibernica has the branches in one plane all lying flat on the surface of the leaf, like a brittle star if you know what I mean.