Concerned members of the public called 999 after spotting a man carrying a gun in Blackburn town centre on Monday (February 28).
Officers found a BB gun was located "down the front of his trousers" after stopping and searching the man.
The man was arrested and interviewed and is due to appear in court charged with a firearms offence.
A spokesman for Lancashire Police said: "Do you think it's acceptable to walk around Blackburn Town Centre carrying this in your waistband?
"Neither do we!
"Lancashire Police will not tolerate this behaviour and will endeavour to prosecute any offenders who think this is acceptable."
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