Cunningham defected to Reform UK in June 2025.[15] She said the Conservatives had "let the country down" on issues such as taxation and immigration.[15] The leader of the Conservatives on the council, Paul Swaddle, said that Cunningham had frequently been late or absent and had lost their trust since the Rotherham decision; she denied the allegations.[15]
Due to making political remarks to The Standard whilst still a CPS prosecutor in June 2025, Cunningham drew controversy as prosecuting lawyers are expected to not take part in "any political or public activity which compromises, or might be seen to compromise, their impartial service to the Government of the day or any future Government".[16] This led to her resignation from the CPS, which was immediately accepted; she would likely have faced disciplinary process if she had not resigned.[7]
After defecting, Cunningham was mentioned by BBC News, The Daily Telegraph and The Times as being a potential Reform UK candidate for mayor of London in 2028.[9][8][17] She criticised incumbent Sadiq Khan over knife crime in London.[8]
In August 2025, Cunningham was one of the launchers of Women for Reform, alongside Mayor of Greater Lincolnshire Andrea Jenkyns, Sarah Pochin MP, and leader of Kent County Council Linden Kemkaran.[18]
On 7 January 2026, Cunningham was announced as the Reform candidate for the 2028 London mayoral election.[19] Cunningham proposed giving priority in social housing to British citizens,[20] and abolishing the Ultra Low Emission Zone.[21] Having been criticised by some on the right for having attended a Pride parade, Cunningham said "I've always been very pro gay rights, and I'll always march for that".[6] In February 2026, after former Reform UK MP Rupert Lowe established Restore Britain, Cunningham described the party as "neo-Nazi". Lowe responded by stating that he had consulted his legal team and called on Cunningham to issue an apology and full retraction.[22] In response to her remarks, Elon Musk, who had endorsed Restore Britain, accused Reform UK of wanting "race extinction".[23]
She did not stand for re-election in the 2026 Westminster City Council election.[24]