Fifteen senior Scottish National party politicians, including the chair of Holyrood’s equalities committee and three government ministers, have warned against a “rush” to alter legislation they believe could change the definition of male and female.

While the equalities secretary, Shirley-Anne Somerville, has said “no one is proposing to change the definition of male and female”, an open letter warns conflation of sex with gender identification “affects a wide range of policy and service delivery, including data collection, education, health and social care, justice and sport. New information about this topic is emerging all the time and deserves to be properly scrutinised.”

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Urging caution that policymakers “are only now developing an understanding of the implications of self-definition of sex”, the letter is the latest salvo in an ongoing and uncharacteristically public row within the SNP regarding two increasingly controversial pieces of legislation.

The SNP manifesto commitment to alter the Gender Recognition Act 2004 (GRA), which would allow transgender individuals legally to change gender by statutory self-declaration, as has happened in Ireland since 2015, has faced opposition from women’s groups who argue it could adversely affect existing equalities provision and the use of women’s services.

Earlier this year, a highly critical report on proposed changes to Scotland’s census – such as adding a third non-binary alternative to the male/female sex question – found a serious lack of consultation with women’s groups had led to the publication of legislation that was “not fit for purpose” and conflated sex and gender identity.

Two of the signatories to the open letter, published in the Scotsman on Wednesday, took part in an exchange of private messages that was leaked last week, which claimed the first minister, Nicola Sturgeon, was “out of step” with her party’s views.

Following the leak, Somerville wrote an article reaffirming the Scottish government’s commitment to transgender rights, while insisting those raising genuine concerns about a conflict with women’s rights “shouldn’t suffer kneejerk accusations of transphobia”.

Although the consultation on the GRA proposals ended last autumn, plans were not included in this Holyrood term’s programme for government, which has been taken by some as an indication of the concern within the SNP. The director of Stonewall Scotland, Colin Macfarlane, has warned the lack of response is causing “real anxiety among trans people”.

James Morton of the Scottish Trans Alliance said Scotland was falling behind other countries in terms of LGBTI equality standards, while underlining that the proposed alteration to the GRA “will not change the definition of male and female”.

Morton added: “We welcome parliamentary scrutiny of the legislation. We had a robust debate about equal marriage, and reform of the Gender Recognition Act should be no different. This will enable parliamentarians to be reassured that there will be no unintended consequences.”