Ministerial responsibility is one convention with two halves. Individual Ministerial Responsibility (IMR) says a minister is answerable to Parliament for their own personal conduct AND for the work of their department. Collective Ministerial Responsibility (CMR) says the whole cabinet must publicly support every government policy or resign.
Both halves are conventions, not statute. They are enforced by political practice (the Whip system, party loyalty, public expectation, the PM's authority) rather than by courts. The Ministerial Code - written rulebook for ministerial conduct, first published 1992 and updated by every new PM - is the closest the conventions get to a formal text.
The case for the conventions is that they hold ministers and the cabinet accountable to Parliament between elections. The case against is that they depend on PM enforcement and political will, so they bite or do not bite based on who is in charge rather than on the wrong itself.
IMR has two strands. The personal-conduct strand still bites: ministers who mislead Parliament, breach the Ministerial Code, are caught bullying, leak sensitive material, or are found financially compromised tend to resign or get sacked. Amber Rudd 2018, Damian Green 2017, Priti Patel 2017, Liam Fox 2011, Dominic Raab April 2023, Suella Braverman October 2022 all went on personal triggers.
The departmental-failure strand rarely bites. The standard exam example is Lord Carrington 1982 (Falklands invasion) precisely because there are almost no modern equivalents. Theresa May survived multiple Home Office failures 2010-16; Gavin Williamson survived the 2020 A-level algorithm fiasco; Boris Johnson as PM survived being the first sitting PM fined for breaking the law.
CMR has been formally suspended twice. The 1975 EEC referendum saw Wilson allow cabinet ministers to campaign on opposite sides - including Tony Benn for No. The 2016 EU referendum saw Cameron repeat the move - six cabinet ministers (Johnson, Gove, Iain Duncan Smith, Patel, Whittingdale, Villiers) campaigned Leave from inside cabinet.
Outside those suspensions the convention works unevenly. Strong PMs enforce it: Thatcher in her prime, Blair in the early years, arguably Starmer in 2024-25. Weak PMs see routine leaking and open briefing against the leader: Theresa May post-2017, Johnson post-Partygate, Truss across her 45 days. The Truss collapse is the textbook case - cabinet ministers were briefing against her in public before she resigned.
Where CMR still produces resignations the form is usually a constructive resignation on principle. Robin Cook 2003 (Iraq) is the textbook. Clare Short followed two months later. Suella Braverman was sacked rather than resigning when she publicly breached the line on Met policing in November 2023.