Images from the scene show firefighters working above the White Rose charity shop.
Monaghan told the BBC firefighters searched the building for any people inside, but no one was found. The fire was extinguished within 15 minutes of the service attending.
He added: “When I attended there was smoke issuing from the roof of the building which was coming from a broken window and the smoke from the fire on the second floor was percolating out of the roof.”
The station manager confirmed the adjacent premises were evacuated and the White Rose shop was not able to start trading, but said the owners told the service no fire or smoke had spread into their property.
He added Friar Lane was expected to re-open shortly.