Although active in Trotskyist politics in the late 1940s, Derer became politically inactive until he and Vera joined the Labour Party in 1964. In the years that followed they became increasingly disillusioned in the way the Leadership and Labour Government operated, being specifically angry at the way Harold Wilson, the Leader of the Opposition, had rejected a policy document drawn up by the Party's National Executive, which called for the state to take a controlling interest in 25 major companies, and which was passed at the 1973 Annual Conference. The Campaign for Labour Party Democracy (CLPD) was formed in 1973 by a group of rank-and-file activists, with the support of about 10 Labour Party MPs.
The first President was Frank Allaun. The main motivation for the Campaign was the record of the Labour Governments in the 1960s and also the way that Annual Conference decisions were continually ignored on key domestic and international issues. The CLPD's first demand was, therefore, for the Open Selection of MPs so that they would be under pressure to carry out Conference policies.
This objective was achieved in 1979/80 through the overwhelming support of CLPs and several major unions, especially those unions where the demand for re-selection was won at their own annual conferences (e.g. TGWU, AUEW, NUPE). CLPD also sought to make the Leader accountable through an election by an electoral college involving MPs, CLPs,, and Trade Unions. Hitherto Labour leaders were elected by MPs alone. This demand was achieved in January 1981. CLPD also promoted a range of reforms to give Labour women and black members greater representation within the Party. In the early 1980s, there were only 10 women MPs, and none at all from ethnic minorities. The main demand for a woman on every parliamentary shortlist was achieved over the period 1986–1988. CLPD sometimes promoted seemingly non-democratic issues such as the significant extension of public ownership, defending the welfare state, and the first-past-the-post electoral system (Derer believed that PR would mean no majority Labour Governments). All such policies derived from the CLPD's commitment to socialist values and socialist advance.
An important pillar of Derer's strategy was to blend representation and participation, whereby the elected representatives (e.g. MPs and councillors) were to be transformed into effectively being a delegate of the party members, focusing on implementing the manifesto on which they had been elected.
Tactics were primarily based on first producing model constitutional rule changes and motions and campaigning nationwide for CLP branches and general meetings to support these and submit them to be voted on at the Annual Conference.
The Derers’ home in Golders Green became a centre of political activity including meetings, planning, printing and administration to help further the campaign, which was supported by hundreds of Labour Party activists in both CLPs and affiliated trade unions throughout the country. Regular communication with supporters was considered (and remains) a key aspect of campaign work. Examples included a campaign newsletter and, at the Annual Conference, a daily information, news, and conference guide sheet (called the ‘Yellow Pages’) produced for conference delegates by a CLPD team, often working until the small hours of the morning. The CLPD also staged fringe meetings at conferences to help galvanise support for key reforms and provide commentary by well-known speakers on the left in the Party and unions on political issues of the day. These were attended by hundreds of activists and delegates. These conference activities are still maintained today.
Although Derer firmly believed in Socialist principles, he could also exercise pragmatism and compromise when that was necessary to further the long-term strategy of the Labour Party, becoming a transformative movement based on grassroots democracy, inclusiveness, and diversity. This involved striving for a united Left and reaching out when necessary to those members in the centre of the Party and affiliated trade unions when their support was critical for obtaining sufficient support for key reforms or elections.
For instance, Derer had a central role in setting up the politically successful Centre-Left Grassroots Alliance (CLGA) of centre left and left groups and organisations in the Labour Party. From 1997, Members of Parliament and MEPs could no longer stand for the six CLP section seats on the NEC, the Party's ruling body, leaving other Labour Party members to contest these seats. The CLGA supported slate of activists won two thirds of the seats, helping the Left to retain a foothold in the Party during a period when New Labour and its centrist policies were in the ascendency. The Derers were also active in the east European solidarity campaign. From 2005 onwards the Derers, after over 30 years of tireless work in the Campaign, wound down their involvement, although Derer retained the role of political secretary. In his later years he became a carer for Vera.