A process of UK energy policy review in the early 2000s has seen renewable energy technologies moving from the policy margins to centre-stage. The review process drew on international experiences of renewables innovation, including an innovation systems framework that emphasises ‘social capital’ (collaborative learning between distributed agents). However, the UK energy system reflects a longstanding policy commitment to ‘financial capital’ (market competition and avoiding ‘picking winners’). This paper analyses policy tensions between social and financial capital by focusing on marine energy innovation, especially in the emerging Scottish policy arena. Recent initiatives to promote renewables innovation in the UK, though significant, face continuing challenges.