Who has power in the construction of economic news in the United Kingdom? Are social media reshaping how this power is enabled? We examine the public Twitter interactions between journalists, political elites and, what is arguably the United Kingdom’s most important think tank, the Institute for Fiscal Studies (IFS), during the 2015 UK general election campaign. Combining human-coded content analysis and network analysis of Twitter discourse about the IFS during a 38-day period, we explain how and why the authority of this think tank is being translated to social media. We develop a new, social media theory of ‘primary definers’ and show how the political authority on which such roles rest is co-constructed and propagated by professional journalists and political elites. Central to this process is a behaviour we conceptualize and measure: authority signalling. Our findings call into question some of the more sanguine generalizations about social media’s contribution to pluralist democracy. Given the dominance of public service broadcasters in the processes we identify, we argue that, despite the growth of social media, there can be surprising limits on the extent to which contemporary media systems help citizens gain information about the assumptions underlying economic policy.