He was first elected to Parliament in 1970, and served as a minister under Harold Wilson and James Callaghan. During opposition he was in the Shadow Cabinet for fourteen years. He was seen as a figure on the left and an ally of Tony Benn and stood as the left's candidate against Roy Hattersley in the 1983 leadership election.
Since then he lost some of his reputation as a firebrand, enough that Tony Blair felt able to appoint him a junior minister at the Department for the Environment. He was sacked in June 2003, and since then has attacked the government on a number of issues, notably the Iraq war and genetically modified food.