I know exactly what you mean. These two-piece shafted fixings are used to join adjacent kitchen cabinets together. An M4 hole is drilled through the side wall of adjacent cabinets, the long section is passed through the hole in one cabinet and the threaded stub section is screwed tightly into the internally threaded section.
I'm having difficulty finding them on the Screwfix and B&Q websites, but I know that B&Q stock them. Try asking for cabinet joiner along with my description to a member of staff at B&Q. I'm sure they'll find them in the store.