The Conservative faithful are in Birmingham this weekend for the party conference. But Julie Girling, a party member for four decades and member of the European parliament, will not be joining them.

Last week the MEP for South West England and Gibraltar learned she had been expelled from the party, after clashing with the leadership over Brexit.

It was not a shock. Girling, along with fellow MEP Richard Ashworth, voted last October for a European parliament resolution that the UK had not made sufficient progress in Brexit talks and should not start talks on trade with the EU.

The vote was mostly symbolic, only six Tory MEPs were in the chamber, but when the result emerged, the response was swift. One Tory MP said the MEPs had behaved appallingly, while social media seethed with talk of “traitors” and “remoaners”. Girling and Ashworth lost the Tory whip and Theresa May told parliament she had taken action against “the two Conservative MEPs who voted against British interests”. Finally on Tuesday the two rebels were expelled.

Girling says: “From a purely personal view it’s extremely upsetting … but I feel so strongly about this that I have had to take this route.”

Her vote was never meant as a political statement, she says. “I thought it was fundamentally dishonest to pretend that negotiations have got to the point where negotiations can move to the next level.”

The vote was only a sign of a deeper estrangement between the remain-supporting MEP and a party that had mostly embraced Brexit. Since the decision to leave the EU, she says, “I just felt there is a lack of any space to have discussions around policy and a beginning of an atmosphere of unless you’re 100% with us you are the enemy. The party just has no place for somebody like me who didn’t agree. I am just not allowed not to agree.”

After the June 2016 vote, Girling reluctantly supported the leave result that many of her constituents had voted for. But she was soon alienated when May embarked on a policy of leaving the EU customs union and single market – “the hardest possible Brexit”.

A turning point was the 2016 party conference, where the prime minister declared that anyone who identified as a citizen of the world was a “citizen of nowhere”, which Girling describes as “that nasty speech”, and then a subsequent speech in which May set out her Brexit red lines. “When she first came out with these red lines I was really astonished,” says Girling, who had expected a softer Brexit to reflect the narrowness of the 52-48 result of the referendum.

“I’ve been a member of the party for more than 40 years, and for 38 of those years the party has been pro-Europe. It’s had its difficulties,” she says, recalling John Major’s battles with the Maastricht rebels and David Cameron’s decision to pull out of the mainstream centre-right bloc in the European parliament, the EEP. “Then overnight Mrs May decided ‘we are all Brexiteers now’ and that just is a place I just can’t go.”

Brexit has changed the party in other ways, Girling says, emboldening those opposed to tackling climate change; Tory MEPs have also voted with Hungary’s ruling party in rejecting EU action to safeguard the rule of law.

“I believe in climate change, I believe in social welfare policy” she says. “The movers and shakers of [Brexit], the ones that left and are coming back [from Ukip] are not people who I have very much in common with at all.”

While there is no Conservative equivalent of Momentum, she predicts “a gradual clearing out of the more moderate conservatives”.

Girling joined the Conservative party as a student, starting her career at the carmaker Ford in 1979, the year Margaret Thatcher came to power.

She was an admirer of Britain’s first female prime minister. “I liked her attitude to privilege,” she says. “She really did break down barriers in the Conservative party [on] Oxbridge and Eton, although it’s all come back.” Cameron’s brand of “compassionate conservatism” also appealed to Girling – “domestically he had the right idea” but was “absolutely useless on Europe”. Cameron made a terrible mistake, she says, by pulling the Tories out of the EEP of Angela Merkel and Jean-Claude Juncker, to set up a new group with Polish nationalists and fringe parties.

Cameron ceded too much ground, she says, to the “the monster that is the Eurosceptic party … He got that completely wrong because the more you chuck them the more they grow.”

Girling and Ashworth joined the EPP this year, a move encouraged by continental politicians keen to embrace the symbolism of the British returning to the fold.

A fervent support of the people’s vote campaign, Girling thinks a second referendum is the only way to overturn Brexit. She believes the EU would accept an extension of article 50 if the UK was thinking again, but the difficulty is what happens if the UK seeks to stay in the EU beyond European elections in May 2019, requiring the election of British MEPs.

In that case, the European elections in the UK could be “a proxy referendum on Britain’s EU membership”, she says, although she believes this is not the most likely scenario.

For now, she thinks the prime minister has backed herself into a corner. While many EU diplomats hope May will have room to make compromises after the party conference, Girling is less convinced. “If Theresa May goes to the Conservative party conference and does a load of tub-thumping – which she will – that doesn’t actually free her up afterwards. It makes it worse,” she says.