Bought from the gift shop at the Royal Botanic Gardens in Kew, the killer pencil had been attached to a razor blade, creating a potentially very dangerous weapon.
The bottom end of the pencil had been sliced to create a gap where the blade was wedged in.
Officers in Kingston tweeted the frightening discovery which was made on Friday (February 5) in Kingston town centre.
Kew Gardens say they are not responsible for what happens to items bought from their gift shop.
A Royal Botanic Gardens, Kew, spokesperson said: “We do not bear any responsibility for how products are used once they have been purchased.”
No arrests have been made.