What it means
A British way to insist you're telling the truth, or to push someone else to back what they just said. You can use it before a claim, or throw Swear down? back at someone when their story sounds a bit mad. It's common in youth chat and everyday banter, and if you say it then get caught lying, you look proper stupid.
Usage examples
"Swear down, I clocked him on the Tube with a parrot on his shoulder, like it was normal, just tapping in at Oxford Circus."
"Swear down, I left the keys on the table, I didn't touch your bag at all."
"He told me he'd pay me back, swear down, and then blocked my number."
"Swear down, I saw Zara's ex outside the chicken shop acting like he didn't know anyone."
"You won fifty quid off that scratchcard? Swear down?"
Where it comes from
It grows out of older English ways of swearing an oath to prove you're telling the truth. In modern British slang, swear down became a clipped, everyday formula for putting weight behind what you say or challenging someone else to do the same. It's been especially common in London and wider UK youth speech.
