Siân Berry, Green Party MP for Brighton Pavilion since 2024, inherited the safest Green seat in the country from Caroline Lucas, and she did so as the most institutionally experienced politician her party has ever sent to the Commons. She is also, improbably for a Green figurehead, an Oxford trained engineer.

Born in Cheltenham in 1974, Berry was educated at Pate's Grammar School, one of the most selective state schools in England, and read engineering at Trinity College, Oxford. She came to prominence in 2003 by helping found the Alliance Against Urban 4x4s, a campaign against city SUVs that drew international attention and made her name. Her rise through the Greens was quick: she was the party's Principal Speaker, then its equivalent of leader, in 2006, a role she held immediately before Caroline Lucas, the woman whose Brighton seat she would later take.

Few Greens have run for as much. She stood for Mayor of London three times, in 2008, 2016 and 2020, the last of those producing 7.8 per cent, the best result any Green has managed in a London mayoral contest. She led the party jointly with Jonathan Bartley from 2018 and briefly as sole leader in 2021, before resigning that June over the party's consultation response on the Gender Recognition Act, which she judged too weak on trans rights. She said she had become "exhausted and demoralised by the direction of the Green Party", a rare public airing of the internal tensions the Greens usually keep offstage.

Her record is built on long local service. She was a Camden councillor for Highgate for almost ten years from 2014, and sat on the London Assembly from 2016 to 2024, working through its transport, housing and planning committees on renters' rights, sustainable transport and youth services funding. That is a deeper governing apprenticeship than most new MPs bring, and far deeper than her four Green colleagues.

Brighton Pavilion handed it a fitting reward. She won the selection on 71 per cent of first preferences and the seat on 28,809 votes, 55 per cent, an outright majority of everyone who voted rather than a mere plurality, with a margin of 14,290. On the safest possible Green ground, she has been a disciplined party loyalist: one rebellion in 562 divisions is near total conformity.

The limits are familiar to her party. She is not a Brighton native but a Cheltenham born, London made politician installed in a stronghold, her mayoral campaigns never seriously threatened City Hall, and she now spreads herself across six spokesperson briefs. A 27.3 per cent majority is a commanding personal mandate but not a lever on government. At 51, with the Oxford degree, three mayoral campaigns, the party leadership and eight years in the Assembly behind her, she has more weight than any Green MP before her. The question is focus: whether she identifies the one or two subjects on which ministers come to dread her standing up will decide whether Brighton Pavilion stays a symbolic fortress or becomes a base from which the Greens actually advance.