A dedicated Secretary of State for Women and Girls is essential in the next government to champion and make the changes many “desperately need”, campaigners have said.

An open letter to the major political party leaders urges them to commit to the standalone role in Cabinet which they said would ensure the seriousness of women and girls’ needs is met with “serious political resource”.

The women and equalities portfolio has traditionally been held by ministers with other responsibilities but the letter, co-ordinated by Agenda Alliance, said responsibility for some of the most vulnerable in society should not be a “bolt-on to other more senior roles”.

The alliance, a coalition of organisations representing women and girls with unmet needs, said a dedicated post would enable the most at-risk to be better represented at the highest levels of government.

The letter, sent on Wednesday, stated: “A Secretary of State for Women and Girls would work across government at the most senior levels to reshape public services and embed a preventative approach.

“They should draw together healthcare, education, housing, violence against women and girls and justice policy to deliver lasting change which addresses how women and girls’ problems are often multiple and interconnected.”

Campaigners said too often women experiencing disadvantage and misogyny are “stigmatised, labelled as just ‘victims’, ‘criminals’, ‘bad mothers’, ‘addicts’, ‘poor’ or ‘useless’”.

Such labels “stick” and “ignore the fact that women and girls experiencing multiple unmet needs are whole individuals, who are hopeful, inspiring, joyful, aspirational and caring”, the letter said.

A dedicated secretary of state would be able to work across government departments to “embed early intervention and hold them accountable for ensuring that all policy responds to gender, age, culture and trauma as a matter of course”, the group said, and to work to design solutions alongside women and girls with lived experience, ensuring their voices are included through consultation and in evaluating services.

They would also be able to “champion the sector”, which the campaigners said has endured decades of declining investment in vital services.

The letter, signed by dozens of organisations including the Fawcett Society, Prison Reform Trust and Centre for Mental Health, said: “Women and girls need high-level political advocacy to bring departments together and address the distinct issues the specialist sector supporting them faces.

“We need funding models which embed full-cost recovery, articulate the cost-savings of prevention, and provide ring-fenced resource for specialist and by-and-for organisations.”

Agenda Alliance chief executive Indy Cross said women and girls at the sharpest edge of disadvantage and poverty are facing an “intolerable” crisis, and their needs are not being given the political attention and resources they require.

She added: “The reality is that only a senior standalone Cabinet Secretary of State for Women and Girls will have the clout and time to drive forward the policy changes women and girls so desperately need for a safer, healthier, better future.

“We will work with the next government, whoever that is, to help make this happen.”