Cottrell is the author[5] of the best-selling military history The Anglo-Irish War: The Troubles 1913–23 which challenges traditional nationalist interpretations of the Easter Rising; the role of the Royal Irish Constabulary and the popularity of the IRA campaign whilst supporting the view that the conflict was as much an Irish civil war as a struggle for independence from the UK.[6]
The War for Ireland 1913–23 – Editor and principal contributing author (Osprey Publishing 2009) ISBN978-1-84603-996-6
I Am Soldier – Contributing author (Osprey Publishing 2009) ISBN1-84603-515-5
Lies, damned lies and statistics: a British perspective of policing the Anglo-Irish War. Paper delivered to the Military History Society of Ireland/National Museum of Ireland Conference marking the ninetieth anniversary of the outbreak of the Anglo-Irish War, Dublin, October 2009