Northamptonshire Police Armed Response Vehicle tweeted this morning that the raid happened at the Starbucks drive-thru restaurant in St James Retail Park.
UPDATE: Starbucks has been taped off and CLOSED to the public
"At 0500hrs this morning two armed men went into Starbucks," the statement said.
"They threatened staff with weapons and stole cash. They didn’t account for Armed Officers sat in the Drive-Thru ordering a coffee at the same time."
A spokesman for Northamptonshire Police said a 29-year-old had been arrested on suspicion of robbery and was currently being questioned. A search was taken place for the other man believed to have been involved.
Northants Police Armed Response Vehicle is responsible for responding to Firearms/TASER Incidents and policing the key road network.