The Cabinet is the pre-eminent body of government. Made up of the Prime Minister, the Chancellor and all other Secretaries of State, including other Ministers of 'Cabinet-rank' such as the Chief Whip, any Minister without Portfolio (normally a party chairman) or key Ministers of State (including the Chief Secretary to the Treasury) and the Commons and Lords business managers (the Leaders both Houses), it is the Cabinet's endorsement of decisions as a whole that forms the instrument of government in the United Kingdom.

The key convention for Cabinet Government is that of 'collective responsibility.' This means that all members of the Cabinet must abide by and support its decisions, regardless of their individual view on a specific matter in question. Any member who dissents after a Cabinet decision or who refuses to toe the line would be expected to resign, or at the very least to remain silent on the issue.

Meetings of the full Cabinet are normally held once a week on a Thursday morning, although historically the frequency has varied. The Prime Minister sets the agenda for meetings and chairs proceedings. Members of the Cabinet present papers prepared by their departments to their colleagues for endorsement. The backing of the Cabinet is the strongest endorsement a policy can obtain from government.

Cabinet provides a forum for debate for key government figures, allowing for compromises to be struck, for dissent to be acknowledged and for future policy direction to be considered. The length and content of Cabinet meetings is often taken as an indication of a Prime Minister's style of leadership – whether Cabinet is used as a genuine forum or as a 'rubber-stamp'. Prime Ministers will often seek Cabinet approval for their approaches to ensure all Ministers are 'on-side'.

Minutes are taken, which are distributed to those in attendance and to top civil servants. Votes are not taken, as all decisions are made unanimously and individual opinions are not recorded. Minutes of Cabinet meetings and copies of papers presented are released publicly after 30 years.