British Sikhs are taking the Government to the high court on Tuesday over its "unlawful" refusal to treat them as an ethnic group in the 2021 census.

They claim Government is acting unlawfully by denying the UK's estimated 800,000 Sikhs the right to declare their ethnicity alongside other groups including Afro-Caribbeans, black Africans, Indians, Pakistanis, Chinese, Arabs and gypsies or Irish travellers.

They want a mandatory ethnicity tick box question to be included in the 2021 census, saying it was unlawful for the Office for National Statistics (ONS) to refuse them such a right.

The census provides Government, councils and other local authorities with the information on their local populations that they need in order to help plan, provide and fund services.

In 2011, the UK-wide census recorded about 430,000 Sikhs based on a non-mandatory question about religion.

However, the Sikh Federation, which is bringing the legal action, says not all people who would identify as ethnically Sikh identify as religiously Sikh.

It estimates there are 700,000 to 800,000 ethnic Sikhs in the UK and says it is vital that the ethnic Sikh population is properly accounted for.

Rosa Curling, a solicitor at the London law firm Leigh Day, which is acting for the Sikhs, said: “Our clients have identified a number of flaws within the process for determining whether to include a Sikh ethnicity category in the 2021 Census.