Hi Aragorn, with all respect, this is what Wikipedia has to say:
http://en.wikipedia.org/wiki/British_Cabinet
In the politics of the United Kingdom, the Cabinet is a formal body composed of the most senior government government ministers chosen by the Prime Minister. Most members are heads of government departments with the title "Secretary of State".
Formal members of the cabinet are drawn exclusively from either house of Parliament.
Two key constitutional conventions regarding the accountability of the cabinet to Parliament exist, collective cabinet responsibility and individual ministerial responsibility. These are derived from the fact
the members of the cabinet are members of Parliament, and therefore accountable to it, because Parliament is sovereign. Cabinet collective responsibility means that members of the cabinet make decisions collectively, and are therefore responsible for the consequences of these decisions collectively. Therefore, when a vote of no confidence is passed in Parliament, every minister and government official drawn from Parliament automatically resigns their role in the executive; the entire executive is dismissed. So, logically, cabinet ministers who disagree with major decisions are expected to resign, as, to take a recent example, Robin Cook did over the decision to attack Iraq in 2003.
Recent custom has been that the composition of the
Cabinet has been made up almost entirely of members of the House of Commons. Two offices — that of Lord Chancellor and Leader of the House of Lords — have always been filled by members of the Lords, but apart from these it is now rare for a peer to sit in the Cabinet. The only current exception is the Secretary of State for Constitutional Affairs, Lord Falconer of Thoroton.