This article analyses the implications of long-term low-carbon scenarios for the UK, and against these it assesses both the current status and the required scope of the UK energy policy. The scenarios are generated using the well-established MARKAL (acronym for MARKet ALlocation) UK energy systems model, which has already been extensively used for UK policy analysis and support. The scenarios incorporate different levels of ambition for carbon reduction, ranging from 40% to 90% cuts from 1990's level by the year 2050, to shed insights into the options for achieving the UK's current legally binding target of an 80% cut by the same date. The scenarios achieve their carbon reductions through very different combinations of demand reduction (implying behaviour change) and implementation of low-carbon and energy efficiency technologies on both the supply and demand sides. In all cases, however, the costs of achieving the reductions are relatively modest. The ensuing policy analysis suggests that while the cuts are feasible both technically and economically and while a number of new policies have been introduced in order to achieve them, it is not yet clear whether these policies will deliver the required combination of both short- and long-term technology deployment, and behaviour change for the UK Government's targets to be achieved.