For any pledge that is part of the published party manifesto, that was in place at the election where the government came to power, if that pledge is subsequently broken, a general election should be triggered.
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The UK public expect and deserve the highest standards of integrity from its politicians and in recent years manifesto pledges have been broken.
Manifesto pledges are one of the main reasons voters choose a particular political party so if the pledges are broken, the voters must be afforded an opportunity to vote again.