A woman in her 60s was walking along Granville Street with her husband when a man approached them at around 4.20pm on Tuesday (February 8.).
The man – later identified as 18-year-old Kevin Pohlodko – snatched the victim's handbag before fleeing the scene, dropping a knife as he ran towards Keighley Road.
The victim tried to chase after Pohlodko but was told to stop by her husband after he had found the defendant’s large black sheathed knife.
DC Claire Rigby, of East CID, said: “This was a despicable offence committed against a vulnerable victim in broad daylight.”
The handbag contained the victim’s Samsung Galaxy phone, cash and credit cards.
Pohlodko and co-defendant Sammy Clark used the cards to buy meat, food and cigarettes.
Clark sold the victim’s phone for just £20.
They used the proceeds from the crimes to buy drugs, police said.
Pohlodko, of no fixed address, was arrested and later charged with robbery, possession of a knife and fraud.
Officers said he denied any involvement in the offences during a police interview, but pleaded guilty to robbery and possession of a knife when he appeared at Crown Court last week.
He was sentenced to two years in jail.
Clark, 31, of Cleveland Street, Colne, pleaded guilty to handling stolen goods and fraud.
He was given a community order.
“Lancashire Police takes a zero tolerance stance to people who arm themselves with weapons,” DC Claire Rigby added.