A group of men were caught stealing thousands of pounds of goods from stalls at British Moto Gp at Silverstone.
A Moto GP fan spotted the group operating at the circuit and took a photograph of them which they passed on to police at the circuit.
Officers were deployed across the circuit on Saturday (August 26) before DS Hayley Thurston and DS Johnny Campbell arrested four men, who are all from Northern Ireland, in possession of stolen items.
A subsequent search of their hotel in Milton Keynes led to the arrest of a fifth man from Northern Ireland and the recovery of an array of further stolen goods, including Moto GP shirts, baseball caps, jackets, fidget spinners and even a framed picture of Spanish Moto GP rider Marc Marquez.
Three Belfast men, aged 74, 54 and 58, a 59-year-old man from Bangor and a 54-year-old from Londonderry have been arrested on suspicion of theft and are being questioned by Northamptonshire Police.
Superintendant Chris Hillery, who is leading the police operation at the Moto GP, said: "We are grateful to the witness who made us aware and I'm delighted our officers responded so quickly to bring these men into custody.
"The overwhelming majority of visitors have come to enjoy a great weekend of motorsport in Northamptonshire, but our officers on the ground are here to protect people from harm and to root out any criminality. This was an excellent piece of police work."