An unwritten rule of British cabinets is that even when individual ministers disagree with a given policy, they still must appear unified and take responsibility for it. This is known as:

Cabinet collective responsibility.

Explanation:

Cabinet collective responsibility, also known as collective ministerial responsibility, is an informal agreement where all the members of the Cabinet have to support the collective decision made by the Cabinet. In other words, even if a member does not agree with the decision made, the person must publicly support it. Otherwise, he or she has to make his or her disagreement public and resign. The reason why they have to quit is that the person does not agree with the decision that the Cabinet, which is represented by a political party, thinks is the best, and it is not correct to work for something that you believe is wrong.

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