From 1989 to 1998 he was a Labour Party member of the European Parliament, and spent five years as President of its Human Rights Subcommittee. In 1998 Coates was expelled from the Labour Party because he left the Party of European Socialists to join the European United Left/Nordic Green Left in the European Parliament, after criticising New Labour's move to the right.[2][4]
It was while a member of the European Parliament that Coates was in contact with Vadim Zagladin, one of Mikhail Gorbachev's advisors, about the idea of a joint meeting between the European Parliament and the Supreme Soviet. Coates persuaded the European Parliament to explore the possibility of such a joint meeting, as a practical way of exploring Gorbachev's call for a ‘common European home’ and supporting his democratic reforms. Eduard Shevardnadze, the Soviet foreign minister, visited the European Parliament, and said he would be willing to be present at a joint meeting. Coates visited Zagladin in Moscow, who offered a four-point programme of stages for realisation of the Joint Special Session, as it came to be known.[5][6]
Coates pioneered a number of initiatives to help focus the institutions of European civil society beginning with a very successful Pensioners’ Parliament, and also including a special Parliament of Disabled People, and two Europe-wide conferences of unemployed people. He strongly supported the Delors programme for full employment in Europe, and became rapporteur of the Parliament's Temporary Committee on Employment, which carried two major reports with almost unanimous support of the European Parliament.
Coates was the co-author, with Tony Topham, of the official history of the Transport and General Workers' Union, among numerous other books on poverty, political philosophy, democratic and humanistic socialism, social and economic issues, peace and disarmament as well as on democracy and human rights. His book The Case of Nikolai Bukharin (Nottingham: Spokesman, 1978) is regarded by some to have served as the international basis for the rehabilitation of that Bolshevik leader. He also continued to support the democratic left in Eastern Europe, and was a member of the advisory board of the Novi Plamen magazine.
Coates was special professor in the Department of Adult Education at the University of Nottingham (1990–2004).