What it means
An unexpected problem that messes up a plan or stops things running smoothly, like chucking a tool into a set of gears. Used when something small turns into a proper headache, from cancelled trains to a mate bailing last minute. Often shortened to just a spanner once everyone knows what’s gone wrong.
Usage examples
"Supplier’s bailed and now the site’s waiting on parts, boss is fuming. Proper spanner in the works, so we’re off to the caff for a brew."
"Everything was sorted for the wedding, then the caterer rang to cancel and threw a right spanner in the works two days before."
"We were dead on schedule until the new software update threw a spanner in the works and crashed the lot."
"We had the whole pub quiz team sorted, then Dan texted saying he was stuck at work. Bit of a spanner in the works, that."
"Was gonna be a quick five-minute fix till the boiler packed in and threw a proper spanner in the works."
Where it comes from
This one comes straight from British mechanical talk. A spanner is what Brits call a wrench, and if you lob one into moving machinery, the whole thing jams and grinds to a halt. That image stuck, so now it means any snag that suddenly gums up the plan.
