The food processing and manufacturing industry is the UK's largest manufacturing sector and consequently a large consumer of natural resources and source of environmental impacts. Considerable research effort has been made to quanitfy and characterise food waste and energy consumption from the industry, enabling the sector to set targets for reductions which contribute to national targets and the UN Sustainable Development Goal 12.3, and to identify improvement measures to meet the targets. A gap in this research is a detailed estimation of the energy consumption which could automatically be avoided through preventing food waste in food manufacturing. This paper reports research which estimates the energy embodied in preventable manufacturing food waste in the UK using available data for 2014. Whilst the estimate of 106 GW h per year is a tiny proportion of the industry's annual energy consumption, it is 1.75 percentage points of the main 20% energy efficiency improvement target and over half the contribution expected from energy management measures to improve energy efficiency. Preventing food waste in the factory could therefore also contribute significantly to energy efficiency and climate change targets with no extra effort.