The incident began at around 12.30pm and has seen police flood the area, closing off certain sections.
According to reports, police were called following a suspicious letter addressed to an unnamed peer in the House of Lords.
A mystery ‘white powder’ was in the envelope, witnesses claim, causing much of Parliament to go into lockdown.
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Members and peers are currently being kept away from the investigation - locked on a terrace.
Police confirmed they were investigating a suspicious package delivered to Parliament at around 12.30pm.
Nobody has been injured or taken ill following the discovery.