Apparently this has been an unusually intense season for landslides in the UK. The rash of collapses was punctuated on Monday by the death of a young woman in Dorset who was walking on the beach at Burton Bradstock when the cliff tumbled down upon her. The problem appears to be heavier rains than usual.
Rain causes landslides by two mechanisms, one obvious and the other more potent. First, rain weighs down a slope by filling the pores in the ground with water instead of air. That's a short-lived fluctuation because the water swiftly drains, but when every other factor inclines the same way it can be the proverbial last straw.
Second, rainwater becomes groundwater, and after prolonged periods of rain and the pores fill up, the weight of that water exerts pressure on its surroundings in all directions. In cliffs and steep slopes, pore pressure pushes sideways against the free face with nothing to oppose it. Raise that pressure enough, and it will overcome the resistance of rotten rock or loose sediment, and you have a landslide. Pore-water pressure is the real culprit. See this item in the Guardian for more details of British landslide geology. And I can show you more landslides in this gallery or give you the basics in this article.
Draining pore water from a landslide Geology Guide photo