The Green party has unseated Labour from mayoral power in the east London borough of Hackney after 24 years.

The new mayor, Zoë Garbett, told reporters she was “elated” and promised that Hackney was just the beginning for the party after it won with 35,720 votes to Labour’s 26,865.

“Across London and the country, people have made it clear that they are desperate for an alternative to this failing Labour government” she said. “It’s not old politics, that parties versus new parties. This is about a system of fear versus a movement of hope.

“All the work I’ve ever done has been to change the system and services that let people down, harm people, and widen inequality. Our borough has over a quarter of a million people,” added Garbett, who succeeds the Labour mayor Caroline Goodley.

“So many people have been failed by the government and the systems, whether it’s parents, migrants, trans people, disabled people and younger people. The list goes on and on.”

Her victory was a massive blow to Labour which is on tenterhooks as the count for the council begins, despite the Greens only holding two of the 57 seats in the borough. A surge in support in the face of dissatisfaction with Labour on issues such as immigration and housing, means a bleak outlook for the party.

The borough is being seen by Polanski as a bellwether for the Greens, with reports that he may use it to launch his own Westminster career in future.