A teenager stopped in Kettering by Northants Police was found to be carrying an 18in-long, 3in-wide machete down his trousers.
The 16-year-old had been stopped and searched by officers from the neighbourhood police team in Kettering as part of the week of action to crack down on knife crime.
He was taken into custody after the blade was discovered.
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Kettering Police Team said: “A routine stop and search turned into something much more, when officers detained a 16-year-old male in the town centre earlier.
“If he had tried to run with this secreted, then he might have lost something... “
And the team added: “The only place he found his way to was to custody where intervention will be offered to prevent any future offending.”