The UK Government is legally committed to achieving an 80% reduction in carbon dioxide emissions compared with 1990 by 2050. The use of scenarios is wide ranging to inform policy development and forming a business as-usual scenario helps to understand possible effects of different policy interventions. However, the term business-as-usual is frequently misused. We show how econo-physical business-as-usual scenarios can be developed by examining the historical behaviour of coefficients which manifest the relationship between components of an economy. We endogenise economic growth by mimicking national level policies that focus on a target level of unemployment. Our case-study demonstrates the ‘trendability’ of coefficients which for one example coefficient is replicated for Australia, Colombia, Taiwan and the USA. We manifest a gross domestic product growth of 2% falling to 1% which contrasts with an exogenous growth of 2.3% of a comparator business-as-usual scenario. We suggest that it may be possible to achieve a greater reduction in the business-as usual carbon dioxide emissions in the UK fifth carbon budget than currently projected.