The damage at the office for UKIP MEP for the East Midlands Margot Parker in the High Street in Corby Old Village is thought to have taken place on Friday night, although was not discovered until Saturday.
A spokesman for Northants Police said: “We had a report of an incident of criminal damage in the High Street.
“It was reported that a window had been smashed.
“It was reported to us on Saturday afternoon, but the exact time of the incident is not known.” The spokesman said a bottle had been recovered from the scene, and it is believed that this was used to smash the window.
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Officers are investigating the criminal damage and any witnesses are asked to call the police on 101.