Police pinned a member of the public to the ground outside the Houses of Parliament today.
Armed police were standing by as the man was searched and removed from the premises.
The man who was dressed in a quilted green jacket, dark jeans and holding a camera bag, was surrounded by seven members of the City of London Police - drafted in to help today.
A Westminster insider said the man had been "behaving strangely".
And officers searching the man were seen taking a pass that would have granted him entry to the public gallery of the House of Commons.
It is thought he may have been attempting to get through the turnstiles from an area of the Parliamentary Estate which the public have access to into the part restricted to pass holders.
He was handcuffed and then led off the estate where he was bundled into a police van.
Parliament is sitting on a Saturday for the first time since 1982 to debate Boris Johnson's Brexit deal.
And Police are particularly on alert because the sitting coincides with a huge People's Vote March, which has already started to descend on Parliament Square.
Tens of thousands of protesters are expected to join the march, demanding a second referendum on the terms of Johnson's deal.
