throw a spanner in the works

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.
See also: spanner, throw, work
Farlex Dictionary of Idioms.

throw a spanner in the works

or

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.
See also: spanner, throw, work
Collins COBUILD Idioms Dictionary, 3rd ed.

put/throw a ˈspanner in the works

(British English) (American English throw a (ˈmonkey) ˈwrench in the works) (informal) spoil or prevent the success of somebody’s plan, idea, etc: Let’s get this finished before the boss comes along and throws a spanner in the works.
A spanner or wrench is a metal tool used for fastening things tightly. The works are the moving parts of a machine.
See also: put, spanner, throw, work
Farlex Partner Idioms Dictionary
See also:
  • put a (monkey) wrench in(to) the works
  • put a spanner in(to) the works
  • put/throw a spanner in the works
  • throw a monkey wrench in(to) (something)
  • throw a monkey wrench into
  • throw a spanner in(to) the works
  • throw a wrench into the works
  • throw a (monkey) wrench in(to) the works
  • throw a monkey wrench in the works
  • put a spoke in someone's wheel
References in periodicals archive
HER form at the start of her latest gig was not to be sniffed at - but Amy nose how to throw a spanner in the works.
She impresses Tyler during a trial shift and is quickly hired - only for Lucas to throw a spanner in the works.
PAUL Devlin has backed Neil Warnock's Crystal Palace to 'throw a spanner in the works' for Blues on Sunday.
CHASETOWN fully intend "to throw a spanner in the works" of Nuneaton Town's title-chasing machine tonight.
"I want to see basketball in this area improve immensely and I was not going to throw a spanner in the works, not that it was really my decision to make.
VILLA are continuing to plan for a summer tour of the United States, although Martin O'Neill admits that the InterToto Cup may throw a spanner in the works.