London ? Police briefly locked down Britain’s Houses of Parliament on Wednesday after a man sprayed a powdery substance in the main lobby.

The Metropolitan Police said the suspect was arrested after spraying what he claimed was anthrax in the central lobby of the Palace of Westminster, which houses Parliament.

Police said tests indicated the substance was harmless.

Doors to the building were locked for about 15 minutes, with lawmakers and staff stuck inside. Lawmakers continued their debates during the alert, officials said.