[9] In September 2019, she successfully challenged the government's prorogation of Parliament, formally supported in the legal case by the former prime minister Sir John Major and the shadow attorney general, Shami Chakrabarti.

[14][18] When she was 14, Guyana introduced strict currency controls that prevented their parents from continuing to send funds for Gina and her brother, so she took a summer job as a chambermaid in an Eastbourne hotel.

[16][24] She has been a leading campaigner against hidden charges in pensions and investment and what she has described as "flagrant mis-selling within the asset management market".

She set up Miller Philanthropy (rebranded to the True and Fair Foundation) in 2009 (which closed in 2019[25]), and established MoneyShe.com in 2014, as a female-focused investment brand.

[27] Those nominated were chosen by an independent panel with members including former High Court judge Dame Linda Dobbs and former Apprentice winner Tim Campbell.

[25] In January 2012,[23][34] Miller set up the True and Fair Campaign, with the stated aim to "limit the possibility of future mis-selling or financial scandals through greater transparency.

In June 2016, subsequent to the United Kingdom European Union membership referendum, Miller privately engaged the City of London law firm Mishcon de Reya to challenge the authority of the British Government to invoke Article 50 of the Treaty on European Union using prerogative powers, arguing that only Parliament can take away rights that Parliament has granted.

[38] Miller stated in various interviews that her motivations for pressing on with the legal action were upholding Parliamentary sovereignty and democracy.

[41] When closing the hearing, the Court President said that the appeal raised important constitutional issues, and the Justices would take time to give full consideration to the many arguments presented to them, orally and in writing, and they would do their best to resolve the case as quickly as possible.

[43] After the government's appeal was dismissed, the Secretary of State for Exiting the EU formally introduced in Parliament, on 26 January 2017, a bill that, on 16 March, was enacted without amendment as the European Union (Notification of Withdrawal) Act 2017.

[48] A man, aged 55, was arrested in November 2016 on suspicion of racially aggravated malicious communications over threats to Miller,[49] but was later told he would not be prosecuted.

[51] Philipps, of Knightsbridge, London, described Miller as a "boat jumper" and added: "If this is what we should expect from immigrants, send them back to their stinking jungles".

[56] In August 2017, Miller said she had faced continuing threats of acid attacks in recent months, and fears leaving her home.

[57] In October 2019, detectives with the Metropolitan Police launched an investigation into a GoFundMe campaign seeking to raise £10,000 to hire a hitman to kill Miller.

[60] She left Best for Britain after the election, describing it as both "a room full of white males deciding what's going to happen to the country"[61] and "undemocratic".

[64] On 28 August 2019, Miller was one of a number of parties to launch legal proceedings against the Johnson government for advising the Queen to prorogue parliament, claiming to do so was unconstitutional.

[65] On 6 September 2019, the High Court ruled that the advice was not justiciable and dismissed her case, but granted permission to appeal.