The externalization and politicization of policy advice has received an increasing amount of scholarly attention in recent years (see Bakvis 1997; Macdonald 2011; Craft and Howlett 2013). Existing research focusses mainly on the visible actors, such as political advisers (Shaw and Eichbaum 2018), advisory committees (Siefken and Schulz 2013), knowledge institutions (Blum et al. 2017) and lobbyists (Fraussen and Halpin 2017). These actors are interesting because of their potential influence on the policy process in their respective roles as agenda-setters, framers, policy entrepreneurs or legitimizers. They are also important in the sense that they can strengthen or weaken the role and position of traditional political-administrative actors (such as legislators, ministers, civil servants and regulators). However, theoretically and empirically very little is known about the role and influence of the less visible type of actors: external personnel who are hired on a temporary basis as policy or management consultants (but see Howlett and Migone 2013a; Van den Berg et al.