After returning to civilian life, Carter worked for BP between 1970 and 1992, as a general manager in the Shetland Islands and Africa in the areas of exploration, production, trading, marketing, and distribution. From 1993 he was Principal Advisor to En Venture, an environmental consultancy, working as a management consultant on sustainable development for industry in the Caribbean, the Pacific Rim, and Europe, including the Balkans. His experience includes capacity building in the European Union and greenhouse gases,[2] as well as the environmental management system.[5]
In 1986 he received a Certified Diploma in Finance and Accounting from the City Polytechnic, London, and in 2007 Oxford Brookes University awarded him a Certificate in Strategic Environmental Assessment.[2]
From 1997, Carter was a member of the United Kingdom's delegation Technical Committee 207 (TC207) on Environmental Management of the International Organization for Standardization (ISO). He has been responsible for drafting three ISO standards, ISO 14015 (2001), ISO 19011 (2002), and ISO 14064 (2006).[5] The first is a standard on environmental management and environmental assessment of sites and organizations,[6] the second provides guidelines for quality and environmental management systems auditing,[7][8] and the third a specification with guidance at the organization level for quantification and reporting of greenhouse gas emissions and removals.[9]
By 2001, Carter was living in Devizes, Wiltshire, and in that year a new local political party called the Devizes Guardians began to be formed, in the aftermath of the felling of five trees in the Devizes Market Place,[10][11] where Carter's office then was. The party registered with the Electoral Commission on 19 June 2002. In its registration, it named Carter as its leader and chairman.[12]
On 1 May 2003, Carter was elected to Kennet District Council as a Devizes Guardian, for the Devizes North ward, commenting "We have to acknowledge there is an element of protest vote in the support we have had. The question of the future of the hospital has been paramount in the issues expressed by the people we have talked to, with transport coming a close second."[10][13][14] In May 2007 he lost the seat to a Conservative.[15]
On Wiltshire Council, the Devizes Guardians held three seats from 2009 to 2013, and these members formed a political group with Carter as leader.[20] They lost all these seats at the local elections of May 2013.[21] Carter retired as a councillor in May 2021 and from consultancy in 2020.