Question: What act was used against the Briton who fired six blank shots at Queen Elizabeth II in 1981?

Context paragraphs:
George VI and Queen Elizabeth Memorial: The George VI and Queen Elizabeth Memorial, situated between The Mall and Carlton Gardens in central London, is a memorial to King George VI and his consort, Queen Elizabeth The Queen Mother.  Completed in its present form in 2009, the memorial incorporates an earlier, Grade II-listed statue of George VI by William McMillan, unveiled by his daughter Queen Elizabeth II in 1955.  The reconfigured memorial, which includes a statue of the Queen Mother by Philip Jackson, relief sculpture by Paul Day and an architectural setting by Donald Buttress and Donald Insall, was unveiled by Elizabeth II in 2009.

Queen Elizabeth II Golden Jubilee Medal: The Queen Elizabeth II Golden Jubilee Medal (French: "Médaille du jubilé de la Reine Elizabeth II" ) or the Queen's Golden Jubilee Medal was a commemorative medal created in 2002 to mark the fiftieth anniversary of Elizabeth II's accession.  The Queen Elizabeth II Golden Jubilee Medal was awarded in Canada to nominees who contributed to public life.  The Queen's Golden Jubilee Medal was awarded to active personnel in the British Armed Forces and Emergency Personnel who had completed 5 years of qualifying service.

Queen Elizabeth Hospital: Queen Elizabeth Hospital or Queen Elizabeth's Hospital may refer to one of several institutions named after Queen Elizabeth I, Queen Elizabeth II or Queen Elizabeth the Queen Mother:

Sapphire Jubilee of Queen Elizabeth II: On 6 February 2017, the Sapphire Jubilee of Queen Elizabeth II, marking sixty-five years of her reign, occurred.  The longest-reigning monarch in British history, Queen Elizabeth II was the first British monarch to have a sapphire jubilee.  This Jubilee featured blue stamps from the Royal Mail, commemorative coins from the Royal Mint, and a reissue of an official 2014 portrait of Queen Elizabeth II by David Bailey.  In this official portrait the Queen wears sapphire jewellery which she received as a wedding present from her father.  The Jubilee also involved a gun salute at the Tower of London, a gun salute in Green Park, gun salutes in several other places around the United Kingdom, and the ringing of the bells in Westminster Abbey.  Theresa May, the Prime Minister of the United Kingdom, congratulated Queen Elizabeth II in regard to the occasion, saying in part, "I know the nation will join with me today in celebrating and giving thanks for the lifetime of service Her Majesty the Queen has given to our country and to the Commonwealth."

Marcus Sarjeant: Marcus Simon Sarjeant (born 1964) is a Briton who fired six blank shots at Queen Elizabeth II as she rode down The Mall to the Trooping the Colour ceremony in 1981.

David Kang: David Kang (born 1970) is an Australian barrister.  In 1994, he fired two blank shots of a starting pistol at Charles, Prince of Wales in protest of the treatment of several hundred Cambodian asylum seekers held in detention camps in Australia.

Treason Act 1842: The Treason Act 1842 (5 & 6 Vict.  c.51) is an Act of the Parliament of the United Kingdom of Great Britain and Ireland.  It was passed early in the reign of Queen Victoria.  It was last used in 1981 to prosecute Marcus Sarjeant.

Queen Elizabeth cake: Queen Elizabeth cake is a dessert cake prepared with typical cake ingredients and a shredded coconut icing.  It is sometimes served with tea.  Queen Elizabeth cake is named after Elizabeth II.  It may have originated in 1953 for the coronation of Elizabeth II, and another account holds that it was invented for the 1937 coronation of King George VI and the Queen Mother Queen Elizabeth.

Diamond Jubilee of Queen Elizabeth II: The Diamond Jubilee of Queen Elizabeth II was a multinational celebration throughout 2012, that marked the 60th anniversary of the accession of Queen Elizabeth II on 6 February 1952.  Queen Elizabeth is queen regnant of 16 sovereign states, known as Commonwealth realms, including the United Kingdom.  The only other time in British history that a monarch celebrated a Diamond Jubilee was in 1897, when Queen Victoria celebrated hers.

Australian State Coach: The Australian State Coach is an enclosed, six horse-drawn carriage used by the British Royal Family.  The coach was presented to Queen Elizabeth II of Australia and the United Kingdom as the official gift on the occasion of the Australian Bicentennial on 8 May 1988, and first used in November of that year at the State Opening of Parliament.  The coach was a gift from the Australian people and was designed and built by the coach builder W. J. Frecklington who subsequently built the Diamond Jubilee State Coach for Queen Elizabeth II as a private initiative.  The Australian State Coach is sometimes used at the British State Opening of Parliament and other state occasions involving the Australian or foreign royal families, such as the visit of Queen Margrethe of Denmark in 2000.  As one of the most modern of the royal carriages, the coach is fitted with electric windows, heating and hydraulic stabilisers; it is therefore regularly used for such occasions.  The Australian State Coach is usually kept at the Royal Mews, where it can be viewed by the public.

Supporting paragraphs: Treason Act 1842 Marcus Sarjeant
Answer: Treason Act 1842