The men had reportedly entered the store on Bedford Road, pushed their way behind the till and made off with two boxes of stock, believed to be cigarettes.
Beds police were called at around 5.30pm after the alarm was raised and were quickly on the scene.
Following the incident and witness reports, two men in their 20s – one from Hertford and one from Scunthorpe – and a 17-year-old boy from Hertford were arrested by officers in London on suspicion of burglary.
Two men and the youth remain in police custody for questioning. No one was hurt in the incident.
The store closed after the incident but reopened this morning (April 26)2
A police spokesman said: “If you have any information about this incident, please report this via 101 or using our online reporting form.”