The previous impeachment process is now considered obsolete and can't be used. It's right that ministers can follow convictions to promote even radical or unpopular policy. It's wrong if this gravely undermines, public safety, rule of law or the functioning of democracy.
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In an unwritten constitution these now need more protection.
Impeachment could not be used to bring down ministers because of a belief or policy. There are already democratic means, for MPs, through votes of no confidence and, for the public, through elections.
Our constitution often relies on unwritten conventions which assume decency and fair play in those to whom they apply but this is sometimes the only protection for core democratic values. When conventions are ignored and their purpose maliciously misrepresented elections alone cannot protect them.