Information on the scale of food waste, its sources, causes and associated environmental impacts is critical for devising food waste prevention strategies. A number of studies have focused on these issues, but there are still significant knowledge gaps, both in terms of the amount of food waste generated in various parts of the supply chain and the related impacts. In an attempt to address some of these gaps, this study focuses on food waste in the UK to estimate its quantities along the whole supply chains and to assess the resulting life cycle environmental impacts. Furthermore, the contributions of various food groups to food waste and their impacts in different life cycle stages are also quantified. The findings suggest that 13.1 Mt of food waste is generated annually in the UK across all the supply chain, leading to the greenhouse gas emissions of 27 Mt of CO2 eq./yr. The highest volume of waste is generated in the cereals (31%) and vegetables & roots subsectors (28%). However, meat and fish are the major contributors to the total life cycle environmental impacts, even though they account for only 10% of the overall food waste. Although post-consumer waste has the highest contribution, both in terms of waste quantities and environmental impacts, the contribution of other stages (primary production, food processing and distribution) is also significant. These findings emphasise the need to consider environmental impacts of food waste and engage all supply chain actors in formulating food waste reduction strategies.