Abstract: A fuel pump assembly for a fuel injection system comprises a drive shaft, at least two pump heads each of which is axially displaced along the drive shaft, each pump head having a respective plunger for pressurising fuel within a respective pump chamber, and at least two cams provided on the drive shaft, each of which is associated with a respective one of the pump heads. Adjacent pump heads are offset angularly from one another by an amount sufficient to allow a region of overlap, in an axial direction along the drive shaft, between the adjacent pump heads.