Verb
throw a spanner in the works (third-person singular simple present throws a spanner in the works, present participle throwing a spanner in the works, simple past threw a spanner in the works, past participle thrown a spanner in the works)
(idiomatic, UK) To introduce a problem, dilemma or obstacle, something unexpected or troublesome.
Halfway through the production of Macbeth, the director found that the stage was smaller than he had expected. This really threw a spanner in the works.
Synonyms: (US) throw a wrench in the works, throw a wrench in the gears, throw a monkey wrench in the works, gum up the works