Allen is a Research Fellow within, and a co-director of, the Tobacco Control Research Group (TCRG). His research has primarily focused on investigating the illicit tobacco trade and the relationship that major transnational tobacco companies have with it. This involves exploring the strategies and tactics that tobacco companies use to try and influence policy to address the illicit tobacco trade and the role that tobacco company business practices play in facilitating the illicit tobacco trade. In addition to these broader aims, his research also involves estimating the scale and nature of illicit tobacco trade in various countries (eg. in Malaysia and Ghana). More recently, he has begun to broaden his research focus to explore tobacco industry influence over broader tobacco control policy. Geographically his work focuses largely on the UK, the European Union, as well as Africa, and the Middle East.