throw a spanner in(to) the works

To disrupt, foil, or cause problems to a plan, activity, or project. Primarily heard in UK. We had everything in line for the party, but having the caterer cancel on us at the last minute really threw a spanner in the works! It'll really throw a spanner into the works if the board decides not to increase our funding for this project.

throw a spanner in the works

put a spanner in the works

BRITISH

COMMON If someone or something throws a spanner in the works or puts a spanner in the works, they cause problems which prevent something from happening in the way that it was planned. If they're suddenly going to change the arrangement, it's going to throw a spanner in the works. It is clear Britain could have put a spanner in the works of the contract. Note: You can also just talk about a spanner in the works, meaning `a problem that prevents something from happening the way that it was planned'. Another possible spanner in the works is the weather, which may prevent us from travelling on the 18th. Note: The usual American expression is throw a wrench into the works or throw a monkey wrench into the works.