A knife with a nine inch blade was discovered by police after they arrested a man for drink driving in Wisbech.
Officers on patrol saw a white Ford transit van hit a road sign while it was reversing in Coblands.
Police spoke with the driver who admitted he had been drinking.
The driver failed the road side breath test blowing 48 - whereas the legal limit is 35.
The man was arrested and a large knife was also seen in the door bin of the van.
A police spokesman said: “We were called at around 12.40am this morning (August 2) to reports that a van was driving erratically on the Coblands, Wisbech.
“A 31-year-old man from Wisbech was arrested at the scene on suspicion of drink driving and remains in custody at King’s Lynn Police Investigation Centre.
Inquiries are ongoing this morning.
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