The MP, who has previously described herself as a "tough old bird", stopped a drunk man as he allegedly fought with two members of staff at a Pret a Manger in Westminster, central London.
The veterans minister, a former TV presenter who once worked for the old Grampian TV in Aberdeen, reportedly stood between the group before blocking the man from returning to the cafe.
She told The Sun: "I shouted at the drunk guy, 'stop it, stop it now'. They often listen to women because they don't expect it.
"It was only afterwards that I thought perhaps that wasn't the brightest thing to do."
A spokesman for the Metropolitan Police said a man was arrested on suspicion of assault following the incident in Horseferry Road at around 7am yesterday.