From there:
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Under the current rules of the 1922 committee, if he wins this evening the prime minister cannot face a vote of confidence for another 12 months. However, these rules can be changed by the executive of the 1922 committee. According to The House magazine, “there is no codified rulebook for the 1922 committee.” And the specific process for confidence votes is not publicly available – “it is in Brady’s sole possession.” This means that the committee could change the rules at any time.
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