A watchdog is investigating if an Office for National Statistics (ONS) census produced flawed data on England and Wales's trans population figures.

The statistics regulator stepped in after the ONS reported that 262,000 people identified as a different gender to their biological sex - which is unusually high.

The numbers would mean around 0.5 per cent of the population is trans.

University of Oxford professor Michael Biggs told the Spectator the numbers were “not plausible” as data show those who said they struggled with English were most likely to be counted as transgender.

Overall, people who didn't have English as a first language were five times more likely to say that they were trans.

It's thought the question posed, "Is the gender you identify with the same as your sex registered at birth?”, may have confused non-native English speakers.

Professor Biggs claimed that the question was posed as such after consultation with Stonewall.

Figures produced by the survey showed the London boroughs of Newham and Brent - which both have a significant number of residents whose first language isn't English - recorded the highest proportion of transgender people.

While adults whose main language isn't English made up 10 per cent of the overall population, according to the ONS census, the group made up 29 per cent of the transgender numbers.

It also said one in every 67 Muslim people in England and Wales is transgender.

The survey, which was carried out in 2021, is carried out every 10 years - but this was the first time it had explored gender identity.

Professor Biggs said the ONS had "screwed up", adding authors  “never thought about how a Bangladeshi grandmother or a Hungarian plumber will think about this question”.

According to the Times, the ONS confirmed it is working with the Office for Statistics Regulation and that it is "possible" the question on gender identity might have confused participants.

The Telegraph has contacted the ONS for comment.