spanner in the works

English

Noun

spanner in the works (plural spanners in the works)

  1. (chiefly UK) Something that disrupts smooth operation or functioning.
    Synonyms: (US) wrench in the works, monkey wrench in the works
    The kids' involvement was unfortunately more of a spanner in the works than a helpful contribution toward Daddy's progress on the task, but he gamely pretended to be thankful anyway.