A high pressure fuel pump for an internal combustion engine comprising: a pumping unit comprising a body with a bore therein and a plunger reciprocally movable in said bore, said plunger having a front portion defining, with said bore, a pressure chamber in said bore and an opposite foot portion; drive means for driving said plunger by its foot portion; said drive means comprise a cam ring arranged to be rotatable about an axis, said cam ring having an inner cam surface; said pumping unit is positioned so as to be surrounded by said cam ring with said plunger foot portion arranged to follow said inner cam surface of said cam ring in such a way that the rotation of said cam ring causes said plunger to reciprocate in said bore; comprising abutment means configured to maintain the foot portion of said plunger in driving engagement with said inner cam surface, wherein said abutment means comprise a spacer element extending in the reciprocating direction of said plunger having a length selected in such a way that, in any position of the cam ring, a first end of said spacer is in contact with said foot portion of said plunger, wherein said plunger foot portion rests against said inner cam surface via a skid element, said foot portion being pressed against said skid by the first end of said spacer element; and the second end of said spacer element rests against said inner cam surface via another skid element, characterized in that said pumping unit body has an elongate shape in the reciprocating direction of said plunger; said spacer element is a U-shaped element having two legs united by a transverse bottom section, the outer ends of said legs forming the first end of said spacer element, whereas the second end of said spacer element is formed by said bottom section; said legs of said spacer element are placed on both sides of said body for its axial guiding. a pumping unit comprising a body with a bore therein and a plunger reciprocally movable in said bore, said plunger having a front portion defining, with said bore, a pressure chamber in said bore and an opposite foot portion; drive means for driving said plunger by its foot portion; said drive means comprise a cam ring arranged to be rotatable about an axis, said cam ring having an inner cam surface; said pumping unit is positioned so as to be surrounded by said cam ring with said plunger foot portion arranged to follow said inner cam surface of said cam ring in such a way that the rotation of said cam ring causes said plunger to reciprocate in said bore; comprising abutment means configured to maintain the foot portion of said plunger in driving engagement with said inner cam surface, wherein said abutment means comprise a spacer element extending in the reciprocating direction of said plunger having a length selected in such a way that, in any position of the cam ring, a first end of said spacer is in contact with said foot portion of said plunger, wherein said plunger foot portion rests against said inner cam surface via a skid element, said foot portion being pressed against said skid by the first end of said spacer element; and the second end of said spacer element rests against said inner cam surface via another skid element, characterized in that said pumping unit body has an elongate shape in the reciprocating direction of said plunger; said spacer element is a U-shaped element having two legs united by a transverse bottom section, the outer ends of said legs forming the first end of said spacer element, whereas the second end of said spacer element is formed by said bottom section; said legs of said spacer element are placed on both sides of said body for its axial guiding.