Following the 2016 UK EU Referendum result Tannock wrote three ECR booklets on the critical UK internal and external security implications of Brexit as well as the consequences of Brexit in Ireland. They are published as "Brexit: The Security Dimension" in early 2017, "The Case for a New WEU" in 2018, and a "Hong Kong in Ireland: Northern Ireland's Brexit Opportunity" in late 2018. All these are on his website www.charlestannock.com and available on Google books. In November 2020 he coedited with Alistair Burt the Conservative Group for Europe Publication: "European Britain Global Britain: Foreign Affairs and International Relations Post-Brexit" which sets out a vision for UK working more closely with its EU partners on Foreign Policy, Defence and Security matters globally.