Head of Peatland Ecology and Conservation, Nature Conservancy 1967-73.
Principal Scientific Officer, Chief Scientist's Team, Nature Conservancy Council, 1973-76.
Assistant Chief Scientist, Nature Conservancy Council, 1976-82.
Senior Ecologist, Greater London Council, 1982-86.
Director, London Ecology Unit, 1986-2000.
Head of Environment, Greater London Authority, 2000-2004.
Visiting Professor, University College London, 1994-present.
Honorary Professor, East China Normal University, Shanghai. 1996-2001.
Chairman of Government Working Party on Lead Poisoning in Mute Swans (1980-81).
Natural Environment Research Council, Terrestrial Life Sciences Grants Panel (1984-87).
NERC Special Topic Grants Panel, Agriculture and Environment (1987-88).
NERC Expert Review Group on Urban Environmental Science (1993-4).
Royal Botanic Gardens Edinburgh, Conservation Advisory Committee, 1992-96.
DoE Working Group on Canada Geese (1993-96).
UK Biodiversity Action Plan Steering Group (1994-5). Chairman Sub-Group on Public Awareness, and Sub-Group on Local Biodiversity Action Plans.
UK Biodiversity Group. (1996-2001). Chairman of Local Issues Group (1996-98).
England Biodiversity Group. Chair of urban and development working group. (2002-2005).
The National Forest Company, Board Member and Non-Executive Director, (1998-2004).
Darwin Advisory Committee (DEFRA), 2000-2006; Chair of public awareness working group 2003-2006.
Royal Commission on Environmental Pollution; Expert Advisor on Urban Ecology and Green Infrastructure, 2005-6.
Positions held in Non-Government Environmental Organisations
British Association for Advancement of Science, Biological Sciences, (President, 2000).
British Association of Nature Conservationists (Vice-President, 1981-85).
Ecology and Environmental Studies Society (President, 1999-2001).
Environmental Law Foundation (Advisory Committee, 1991-2000).
Field Studies Council (Executive Committee, 1979-85).
Landscape and Arts Network (Member, 1993-2004; Advisor, 2001-4)
London Biodiversity Partnership (Chair, 1997-2004).
London Ecology Centre Trust (Board of Governors, 1985-91).
Mires Research Group (Secretary, 1968-73).
Royal Horticultural Society, (Science and Horticulture Committee, 1994-2002; Conservation and Environment Committee 2001- 2011).
The Reigate Society (President 1995-2000).
Think Green Campaign (Board of Directors, 1985-91).
Tree Council (Vice-Chairman 1991-92; Chairman 1992-1994; Vice President 2002-6).
Trust for Urban Ecology (Chairman 1987-91; President 1991-94).
UNESCO MAB Committee on Biosphere Nature Reserves.
Task Force on Criteria and Guidelines for the choice and establishment of Biosphere Reserves, Paris 1974; Member of Task Force and Chairman of Criteria Committee; Consultant Editor of Task Force Report.
Member of UNESCO Committee on Biosphere Nature Reserves, Moscow 1982.
European Academy of the Urban Environment Berlin; Member of Planning Committee 1989-91and European Steering Committee 1991-94.
IUCN World Commission on Protected Areas; Member of WCPA 2014; Member of Urban Specialist Group 2004.