formally decline to vote either for or against a proposal or motion:
synonyms: not vote · decline/refuse to vote · sit on the fence
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Given that we are paying our MPS a small fortune I think it is dereliction of duty not to vote. We place them there because we want then to represent us ‘We, the people’. Whilst they do have a mind of their own they are in the house to do what we want!
Abstaining should never be allowed!
PS I forgot to mention cowardly act!