Former Green Party leader Caroline Lucas is stepping down at the next general election.

In a letter sent to her Brighton Pavilion constituents, Ms Lucas said it had been the “privilege of my life to serve this extraordinary constituency and community”.

She said the “threats to our precious planet” had become “ever more urgent”, but that her role in parliament as the Green Party’s only MP meant she had “struggled to spend the time I want on these accelerating crises”.

“I have therefore decided not to stand again as your MP at the next election,” she said.

Ms Lucas, 62, was elected as the MP for Brighton Pavilion at the 2010 general election, becoming the first Green Party candidate to be elected to the House of Commons.

Her share of the vote has increased at every election since, with constituents returning her to parliament with a majority of almost 20,000 in 2019.

In her letter, Ms Lucas said her focus on being “first and foremost a good constituency MP” meant she had “not been able to focus as much as I would like” on climate concerns.

She said: “I’ve done everything possible to help wherever I can and always worked to ensure that people feel heard, that their concerns matter, and that they are not alone.

“But the intensity of these constituency commitments, together with the particular responsibilities of being my party’s sole MP, mean that, ironically, I’ve not been able to focus as much as I would like on the existential challenges that drive me – the nature and climate emergencies.”

She added: “I have always been a different kind of politician – as those who witnessed my arrest, court case and acquittal over peaceful protest at the fracking site in Balcombe nearly 10 years ago will recall.

“And the truth is, as these threats to our precious planet become ever more urgent, I have struggled to spend the time I want on these accelerating crises.”

Ms Lucas was Green Party leader between 2008 and 2012 before returning for a second stint at the helm, this time co-leading the party with Jonathan Bartley for two years from September 2016.

The part’s current leadership heralded her as a “force of nature” and said they would strive to get more MPs to build on her legacy.

Co-leader Carla Denyer said: “Caroline’s impact on politics in this country cannot be overstated: she truly is a force of nature and has been an extraordinary servant of the people of Brighton Pavilion as well as the Green Party. We are so proud of her achievements.”

Adrian Ramsay added: “Very few politicians can claim to have changed the course of the national debate in the way Caroline has. She has brought so much to us as a party, shown real integrity in her work and added a crucial dimension to our democracy in this country.”

He said the party is now “striving to get more Green MPs elected at the next general election so that we can build on Caroline’s achievements”.

Ms Lucas joins a growing band of senior elected politicians who have declared that they will step down at the next election, which is expected to be contested next year.