Dozens of academics have criticised guidance proposing to allow people in the next census to choose whether they are male or female irrespective of their biological sex.

The next census in England, Wales and Scotland is due to take place on March 21, 2021.  It is overseen by the Office for National Statistics, which has said that the question on sex will continue to be binary - offering only male and female as options - but that respondents will be able to answer the question according to their own self-identification.

Parliament is to consider the exact wording of the census next year.

The proposals have been strongly criticised by over 80 academics who have outlined their concerns in a letter to The Sunday Times. 

They fear that permitting sex self-identification will skew the data in a way that is damaging to wider efforts to tackle gender inequality. 

Allowing people to choose the sex they identify with rather than their biological birth sex "will effectively transform the sex question into one about gender identity", the academics write.

"We are concerned that this will undermine data reliability on a key demographic variable and damage our ability to capture and remedy sex-based discrimination and inequality," they say. 

The guidance also proposes a voluntary question about gender identity.

The academics added: "We welcome the decision to include a voluntary question on gender identity in the 2021 census in England, Wales and Scotland. Sex and gender identity are distinct and should not be conflated." 

Signatories of the letter include Professor Alice Sullivan, sociology professor at University College London (UCL), UCL demographer Professor Heather Joshi, and Bristol University statistician Professor Harvey Goldstein.