The Childhood Obesity Plan aimed to reduce sugar and energy in foods through a voluntary Sugar Reduction Programme. Our primary objective was to determine whether this implementation strategy had been successful, focusing on the out-of-home sector. We used a repeated cross-sectional design to evaluate nutritional changes in desserts served by leading chain restaurants. We extracted nutrition information from online menus in Autumn/Winter 2020, for comparison with baseline (2017) and interim (2018) values extracted from third-party datasets. We assessed compliance with the 20% sugar reduction target and category-specific energy targets by product category and for pooled desserts. Overall, sugar/portion and energy/portion decreased by 11% and 4% respectively. Policy targets were achieved in 1 of 5 categories (ice cream: -38% sugar, p<0.001; -30% energy, p<0.001). Secondary outcomes were analysed for subgroups with the necessary data. Few chains significantly reduced sugar and/or energy across their dessert range. Energy/portion was positively associated with portion weight and sugar/portion but not with sugar/100g. More than half of adult desserts contained excessive sugar and/or saturated fat compared with dietary guidelines. Children’s desserts less frequently exceeded guidelines. These results demonstrate that voluntary measures can drive substantial change when technical, commercial and operational barriers can be overcome.