Downing Street is one of the most protected places in the United Kingdom.
The barriers were first used to prevent access to the road in 1920 and were periodically removed and re-introduced over the next 69 years depending on the perceived level of threat.
However, a security checkpoint marked by large black doors has been installed at each end of Downing Street since 1989, introduced amid fears of IRA attacks.
After an IRA mortar attack in 1991, security was further tightened.
The street is constantly guarded by armed policemen from the diplomatic protection group.
There is also usually at least one police officer stationed outside the door of number 10.
To get through the doors, people had to show a pass to one of the officers.
There are also extensive security devices and cameras on the street.
Despite extensive security, protests are still allowed outside the gates as it is seen as an important part of UK democracy.
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However, for security reasons, full details of the protective measures in place around Downing Street and Number 10 have not been made public.
In response to a Freedom of Information request about security around Downing Street, the Metropolitan Police said: “Releasing details of the number of officers deployed, particularly in relation to a specific location or at a specific time, would provide details of police tactics and resources used in relation to security and protection operations.
“This would allow those with criminal or extremist intent to gain an operational advantage over the MPS and thereby undermine the safeguarding of national security and compromise our law enforcement functions.”