Stephen is a Professor of Economics at University College London. After joining the IFS staff, in 1985, he established a research group covering issues of European fiscal policy, environmental taxation, and local government finance, and in 1990 was appointed Deputy Director. He joined the Department of Economics at UCL part-time in 1990, and left IFS to commence a full-time post at UCL in 1997. His main research and teaching interests lie in the fields of environmental economics and taxation. Stephen's work on environmental policy is mainly concerned with the economics of instrument choice in environmental regulation. In the area of taxation he primarily works on the economics of European VAT policy and on excise taxes. Together with co-authors he contributed papers on VAT and on Environmental Taxation to the Mirrlees Review of the UK Tax System, coordinated by IFS, which reported during 2011.