Justine Greening, speaking at the Conservative Party conference in 2017 (Carl Court/Getty)

Former education secretary Justine Greening has announced she will not be standing for the Conservatives in the next election, accusing the party of becoming “the Brexit Party”.

Greening has served the Conservatives since 2006 and became the first cabinet minister to come out while in office in 2016.

As well as education secretary, she was also minister for women and equalities. Her decision to come out publicly on the day of Pride in London led to her winning politician of the year at the PinkNews Awards in 2017.

In an open letter on Tuesday, September 3, she issued a scathing criticism of Boris Johnson’s government, saying she is “deeply concerned” by the party’s approach to Brexit.

My letter to @BorisJohnson on why I’ve decided not to stand for @Conservatives at the next election. It’s a privilege to serve as MP for #Putney #Roehampton & #Southfields. I’ll continue to speak up for our community in Parliament & campaign on #socialmobility with @thesmpledge. pic.twitter.com/CFEMWqsm0s — Justine Greening (@JustineGreening) September 3, 2019

Speaking on BBC Radio 4’s Today programme, the Putney MP accused the Conservative party of “narrowing down its appeal” by moving further to the right. She said a general election would not offer people a “sensible choice”.

Greening’s resignation comes after the government threatened to remove the whip from long-serving MPs if they voted against its Brexit plans. She is among the handful of Tory MPs risking expulsion by backing a bill to block a no-deal Brexit.

She indicated she was not deterred by the threat of dismissal and would be voting for legislation this week to force the government to extend Article 50 rather than take Britain out without a deal.

“It’s very clear to me that my concerns about the Conservative Party becoming the Brexit Party in effect have to pass,” she said.

“Therefore my decision is that if I really want to continue to make a difference on the ground on opportunity and on social mobility, I need to do that outside parliament, and that’s what I’m prepared to do.”

Greening has previously spoken out in support of LGBT-inclusive education and the need for the UK to continue pushing for LGBT+ rights.

Along with most of her Putney constituency, she voted strongly for Remain in 2016.

Supporters have praised her for standing by her principles, but lamented yet another moderate Conservative MP dropping out of parliament over ongoing Brexit negotiations.

Justine Greening tells @BBCr4today she is going to stand down at next election as she reckons she can make bigger difference outside – whatever your politics it’s sad that someone widely respected and experienced thinks they can do more outside Parliament to make change — Laura Kuenssberg (@bbclaurak) September 3, 2019

BREAKING: Justine Greening says she will not stand for the Tories at the next election. Another moderate bites the dust. #r4today — Kevin Schofield (@PolhomeEditor) September 3, 2019

Seriously bad news for the @Conservatives @JustineGreening has been bullied out of Parliament by Johnson & gang. She is hugely talented, state comp educated & a true One Nation Tory. Yet more evidence that the Conservative Party is the Brexit Party. A v sad day. — Anna Soubry MP (@Anna_Soubry) September 3, 2019

Greening said she would continue to be a Tory member and vowed to stay involved in politics, but said parliament had been “stymied” by Brexit.