The Scottish Government is "changing what it means to be female" with its new proposals on the census, academics have claimed.

Dr Kath Murray, of the Scottish Centre for Crime and Justice Research, said asking people what gender they identify as rather than their biological sex was one of a range of policies which were "increasingly confused." 

"This blurring, which has the effect of changing what it means to be female, has implications for the protection of women's rights," she said.

Dr Murray is one of a range of critics who have responded to the government's Census (Amendment) Bill, which is currently being considered by the parliament's Culture, Tourism, Europe and External Affairs Committee.

Changes to the census proposed by the Scottish Government are confused and would render the information it gathers about sex and gender meaningless, according to several academics and feminists.

Read more: Scottish Government's gender self-ID plan "overrides science"

One professor has compared new proposals, which would exclude biological sex from questions being asked at the next Scottish Census, to recording race based simply on whether white people 'believe' they are black.

Other responses to a consultation on the subject claimed the proposals will "change the legal concept of sex in a way that is not consistent with scientific evidence."

Kathleen Stock, a philosophy professor at the University of Sussex, said the changes were a "profoundly misplaced move".

Rosa Freedman, Professor of Law at Reading University said the bill would see the census  conflate sex and gender identity in a way which would have far-reaching impacts both on the data collected and the way sex and gender identity are treated in law.

Read more: Backlash as Edinburgh University Rector Ann Henderson accused of transphobia over tweet

The Scottish Government says its Census (Amendment) Bill is designed to enable details about people's gender identity and sexual orientation to be gathered voluntarily.

Ministers say people are already free to answer a question about sex in the census according to their identity rather than the body they were born with. But if passed, the bill will change the law to explicitly remove the need for the 2021 census to record the biological sex of people who answer.

A policy memorandum published alongside the bill claims that "society's understanding of sex has changed" and points out that the previous census in 2011 allowed people to answer with the sex they identified as. It says the next census needs to be more inclusive still, and will provide for people to answer with a third 'non-binary' option. "Importantly, the sex question proposed will not seek a declaration of biological or legal sex".

Read more: Scottish prison service rejects call for 'transgender wings' in jails

However, many respondents to the Culture Committee's inquiry are warning this will completely change the nature of the census, and failing to collect data about people's biological sex will undermine planning in areas such as equalities, criminal justice, health and education.

Professor Freedman, who will give evidence to the committee today said: "Conflating sex and gender identity will undermine sex as a separate category protected by law." 

She says services and protections - mostly for women - based on sex, need to be preserved, in area such as medical treatment, prisons and refuges, women's sports, religion and youth groups. "Without accurate data from the census, we are concerned that these will be further eroded or undermined," she said.

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Professor Stock said gender identity was a term with "no well-established meaning" and asking people only what they identify as would mean the census ceased to be "scientifically respectable data". She said the Government was confused when it described sex and gender identity as linked. "There are white people that believe they are black. This doesn't show that this belief that one is black is linked to race," she said.

In her submission to the committee she argues the policy makes it clear the original census question about sex is being completely changed. "If it goes through this will be a profoundly misplaced move," she said. "having accurate information about actual sex class is extremely important for tracking all sorts of related statistics to do with discrimination, which will be lost if this move goes ahead."

Read more: Scottish Government's gender self-ID plan "overrides science"

A separate definition of sexual orientation in the policy is "useless," Prof Stock adds, and says women, gay and lesbian and trans people all need protection from discrimination - but the discrimination they experience is different. "We need to preserve these differences, or else the census becomes a pointless exercise."

Supporters of the changes, including Stonewall Scotland, say the opposite  - arguing that changing the census will enable better protection of people who do not identify as their birth gender and will provide information to plan services such as gender identity clinics.

The charity said: "The inclusion of questions on aspects of gender identity, including trans status... could be effective in broadening understanding of trans identities," and added "without firm estimates of the number of trans people in Scotland it is difficult tfor NHS Scotland to plan changes in demand for gender identity services."

Read more: Backlash as Edinburgh University Rector Ann Henderson accused of transphobia over tweet

Stonewall opposes asking people about both their biological sex and gender identity. It said "asking separate questions on sex and gender identity would likely sit uncomfortably with trans respondents." 

Critics of the bill argue it is important to know people's biological sex to plan a host of health services, such as fertility support and prostate cancer care. They also cannot see why it is not possible to ask a question on both sex and gender identity.

Read more: Rise in number of transgender children in Scotland

Dr Murray, of the Scottish Centre for Crime and Justice Research, at Edinburgh University, said understanding of gender and identity had changed but sex as a biological fact had not. "There is no robust evidence to suggest that scientific understanding of sex has changed."

She said the Government had not consulted widely enough on the impact of the proposed changes to the census. "Any further question development on sex and gender should include input from women's groups who appear to have been excluded from the process to date," she said.

Read more: Scottish prison service rejects call for 'transgender wings' in jails

A spokeswoman for  National Records of Scotland conceded that this had not yet been done, but said women's groups and others would now be asked for their views. 

“The purpose of the Census (Amendment) (Scotland) Bill is to make answering census questions on sexual orientation, and certain aspects of transgender status and history, voluntary," she said. "At present there is no current whole population count of the trans community. "

“The Bill is not about the specific questions and wording to be used in the Census as that will be considered by Parliament later in 2019 and views from all groups - trans and women’s groups - will have opportunities to be heard.

“Question work is ongoing and we are engaging with stakeholders on this currently.  Whilst no specific engagement has been carried out with women’s groups so far, this is now underway.”