Trans people will be permitted to change their sex on the next official census, despite warnings it could mean the statistics become “skewed”. Guidance for the forthcoming survey in 2021 will give respondents the option to state their sex is “different from what is on your birth certificate”. It is feared the advice, which applies to both adults and children, could distort population data upon which the Government bases future policy. A set of “rehearsal” questions published by the Office for National Statistics (ONS) this month provided written advice alongside the question on sex It said: “If you are one or more of non-binary, transgender, have variations of sex characteristics, sometimes also known as intersex, the answer you give can be different from what is on your birth certificate. “If you’re not sure how to answer, use the sex registered on your official documents, such as passport or driving licence, or whichever answer best describes your sex. “A later question gives the option to tell us if your gender is different from your sex registered at birth, and, if different, to record your gender.” Explaining why the question is asked, the census form is expected to say the answers helps “charities, organisations, and local and central government to understand what services people might need”. It also can be used to “monitor equality between groups of people of different sexes”, the document continues. The move comes amid a cultural sea change among public bodies about how biological sex is recorded, even if the individual in question has not undergone physical changes. The NHS, prisons and schools have all taken to steps towards allowing people to register as the gender with which they best identify. Dr Juile Maxwell, a paediatrician for the NHS, raised concerns about the implications the move could have for public funding. “Almost every kind of illness behaves differently in men and women,” she told the Mail on Sunday. “If the national statistics are skewed in this way so you don’t know how many biological men or women there are, and if you add on to that the fact people are already changing their sex on medical records, you lose any meaningful knowledge of how often health problems are happening in men and women. “And my biggest fear for children is they are not going to get appropriate health services allocated for their needs because of messing around with statistics.” The census will be sent out to 26 million households - electronically rather than by post for the first time - in March 2021