The assumption that the policy area of security has depoliticising effects has diverted attention from the diverse ways in which parliamentarians are increasingly active on security. This development represents a shift away from the traditional executive-dominated security state and a challenge to security theories that assume security to be characterised by depoliticisation in the form of democratic marginalisation. The security literature assumes parliaments to be at worst irrelevant and at best a variable affecting the decisions of states, governments, and leaders. Analysing the work of UK parliamentary committees from the 1980s to the present, this article presents an original understanding of politicisation that subverts this view. This is politicisation by volume – increased amounts of parliamentary activity – in contrast to the more usually understood qualitative forms of politicisation such as increased polarisation, controversy or contestation (although the different forms of politicisation are not mutually exclusive). The article finds that parliamentary committee activity on security has increased from a base of almost nothing in the 1980s and before to regular and broad engagement in the present.