Question: When did they put gates on downing street?

Disambiguated questions and answers:
context: Barriers were erected at the St James's Park end of the street for the unveiling of the Cenotaph on 11 November 1920. They were a public safety measure intended to prevent the crowds in Whitehall becoming too dense.
question: When did they put barriers on downing street at the St James's Park end of the street?
short_answers: 11 November 1920
wikipage: Downing Street
context: When the movement for Irish independence became increasingly violent, it was decided to retain the barriers, which were raised and strengthened. On 26 November 1920 construction commenced on a wooden barricade, high at the end of the street. They were described as being of a "substantial character" mounted on proper foundations and incorporated vehicle gates. The barriers were taken down in 1922 when the Irish Free State was created.
question: When did they put a wooden barricade on downing street at the end of the street?
short_answers: 26 November 1920
wikipage: Downing Street
context: Vehicle access was curtailed in 1973 when metal barriers were placed across the entrance to the street. In 1974, the Metropolitan Police proposed erecting a semi-permanent barrier between the pavement and carriageway on the Foreign Office side to keep pedestrians off the main part of the street. The proposal came with assurances that tourists would still be permitted to take photographs at the door of Number 10. The Prime Minister, Harold Wilson, rejected the proposal, feeling that it would appear to be an unacceptable restriction of the freedom of the public. Wilson's private secretary wrote "I much regret this further erosion of the Englishman's right to wander at will in Downing Street."
question: When did they put metal barriers on downing street at the end of the street?
short_answers: 1973
wikipage: Downing Street
context: Vehicle access was curtailed in 1973 when metal barriers were placed across the entrance to the street. In 1974, the Metropolitan Police proposed erecting a semi-permanent barrier between the pavement and carriageway on the Foreign Office side to keep pedestrians off the main part of the street. The proposal came with assurances that tourists would still be permitted to take photographs at the door of Number 10. The Prime Minister, Harold Wilson, rejected the proposal, feeling that it would appear to be an unacceptable restriction of the freedom of the public. Wilson's private secretary wrote "I much regret this further erosion of the Englishman's right to wander at will in Downing Street."
question: When did they put a semi-permanent barrier on downing street between the pavement and carriageway on the Foreign Office side?
short_answers: 1974
wikipage: Downing Street
context: In 1982 access was further restricted by railings and a demountable gate. They were replaced by black steel gates in 1989. The increase in security was due to an increase in violence, particularly by the IRA during The Troubles. The Thatcher ministry was particularly moved to increase security after the 1979 assassination of Lord Mountbatten.
question: When did they put railings and a demountable gate on downing street?
short_answers: 1982
wikipage: Downing Street
context: In 1982 access was further restricted by railings and a demountable gate. They were replaced by black steel gates in 1989. The increase in security was due to an increase in violence, particularly by the IRA during The Troubles. The Thatcher ministry was particularly moved to increase security after the 1979 assassination of Lord Mountbatten.
question: When did they put black steel gates on downing street?
short_answers: 1989
wikipage: Downing Street

Long-form answers:
knowledge: content: Access through these gates led to a political scandal known as Plebgate (or Gategate), which started in September 2012. The trigger was an altercation between Conservative Chief Whip Andrew Mitchell, and the police officers on duty at these gates. Mitchell had to resign as the Government Chief Whip because of the incident.
wikipage: Downing Street Security gates
long_answer: Over the course of history, several security measures have been taken on Downing Street. Barriers were erected at the St James's Park end of Downing Street for the unveiling of the Cenotaph on 11 November 1920. These barriers were a public safety measure intended to prevent the crowds in Whitehall from becoming too dense. Then, when the movement for Irish independence became increasingly violent, it was decided to retain the barriers, which were raised and strengthened. Additionally, on 26 November 1920 construction commenced on a wooden barricade, high at the end of Downing Street. This wooden barricade was described as being of a "substantial character" since it was mounted on proper foundations and incorporated vehicle gates. These barriers were then taken down in 1922 when the Irish Free State was created. Later, in 1973, vehicle access on Downing Street was curtailed when metal barriers were placed across the entrance to the street. Then, in 1974, the Metropolitan Police proposed erecting a semi-permanent barrier between the pavement and carriageway on the Foreign Office side to keep pedestrians off the main part of Downing Street. The proposal came with assurances that tourists would still be permitted to take photographs at the door of Number 10. The Prime Minister, Harold Wilson, rejected the proposal, feeling that it would appear to be an unacceptable restriction of the freedom of the public. Wilson's private secretary wrote, "I much regret this further erosion of the Englishman's right to wander at will in Downing Street." Then, in 1982, access to Downing Street was further restricted by railings and a demountable gate. Then, in 1989, these were replaced by black steel gates. This increase in security was due to an increase in violence, particularly by the IRA during The Troubles. The Thatcher ministry was moved to increase security after the 1979 assassination of Lord Mountbatten. In September 2012, access through these gates led to a political scandal known as Plebgate, or Gategate. The trigger was an altercation between Conservative Chief Whip Andrew Mitchell, and the police officers on duty at these gates. Mitchell had to resign as the Government Chief Whip because of the incident.