Armed guards have been deployed on the river Thames to protect the UK's Parliament building in the Palace of Westminster in London after a recent late night mock security exercise revealed the building's weakness via the river, UK media reports have said.
A new river barrier has been recommended after officers posing as attackers used a boat to enter the Palace of Westminster, being able to target around 100 fictional MPs in one go.
A stretch of perimeter fence only three-foot high was identified as another weak spot around the Parliament.
"The security of members, staff and the visiting public is our highest priority," a spokesperson for the Houses of Parliament said.
"We work closely with the police, security services and others to ensure our security measures are effective and meet whatever level of risk Parliament faces. These measures are always, and will continue to be, under constant review," he added.
To maintain secrecy, the security drill was held at night during parliamentary recess, with daytime security conditions were recreated by dozens of staff and volunteers.
The exercise showed that the Thames was a weak spot, with riverside terraces used by MPs and peers.
After arriving by boat the mock terrorists were quickly able to reach the chamber, The Times reported.
In March, Khalid Masood ran over pedestrians on Westminster Bridge before stabbing Scotland Yard police constable Keith Palmer to death at the gates of the Parliament.
Sir Jon Murphy, a former police chief constable, was asked to review perimeter security of the building in the wake of the attack.
His key findings reported by The Sunday Telegraph include a physical barrier known as a boom should be placed in the river to stop boats approaching Parliament.
Such defences are usually floating and some parts of the perimeter are protected by a fence that is only waist high.
There is also some consideration likely to pedestrianising Parliament Square in the heart of London.
Armed guards had already been stationed at Parliament gates since the attack in March.
New passes will be issued to 15,000 people who work in Parliament, with names and photographs on both sides.