An investigation has been launched following an incident at Horse Guards Parade in Westminster on Monday morning.
At around 08:50hrs, a 29-year-old man, who was armed with a knife, confronted two Ministry of Defence Police officers.
Taser was deployed and the man was restrained by officers. There were no reports of any injuries.
He was arrested on suspicion of attempted murder and possession of an offensive weapon and remains in custody at a central London police station.
The incident is not being treated as terror-related.
An investigation is under way. Met officers will continue to liaise closely with the Ministry of Defence Police as it progresses.
Anyone who witnessed the incident, or who has other information which could assist officers, is asked to call 101, providing the reference 1730/18APR.