Change the electoral mandate so the electorate vote both for their local MP and for a PM at General Elections. PM candidate list being open with a requirement for party sponsorship or a deposit, to discourage frivolous candidates.
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The political establishment see an election as being designed to vote a party into power. The electorate vote for their local MP, but their decision is often influenced by who they want be the party in power, and Prime Minister. We want the election process to be reformed to be better aligned with the voting public's perception of the value and purpose of their vote.