He has also held visiting positions at six universities overseas including the Australian National University and recently a Visiting Erskine Fellowship at the University of Canterbury, New Zealand. He has published 66 research papers and his 18 books include The Economics of Taxation: Principles, Policy and Practice (with Chris Nobes) 14th edition, Fiscal Publications, 2014 and A Dictionary of Taxation, 2nd edition, Edward Elgar, 2012. He was also Editor of Taxation, Critical Perspectives on the World Economy, four volumes, Routledge, 2002.