Abstract: A fuel pumping unit has a low pressure pump, a high pressure pump, and a drive input which drives the low and high pressure pumps. The low pressure pump supplies, in use, fuel at a boosted pressure to the high pressure pump. The fuel pumping unit further has a low pressure housing containing the low pressure pump, and a high pressure housing containing the high pressure pump. The housings are joined together at a housing interface. The drive input is contained in one of the housings, whereby drive from the drive input is transferred across the interface to the pump in the other housing. The housing interface includes a gap which interposes between the high pressure pump and the low pressure pump. A layer of substantially stagnant fuel is trapped, in use, in the gap to reduce heat transfer from the high pressure pump to the low pressure pump.