The Office for National Statistics are considering making the sex question optional in the next census in 2021. Here's an article about it: www.telegraph.co.uk/news/2017/10/08/no-sex-census-ons-proposes-making-intrusive-question-voluntary/
So you might be interested in signing this petition, asking for the question to remain compulsory: petition.parliament.uk/petitions/202435
Please sign and share far and wide!