The measure is outlined in a new NHS document for all hospital trusts and local health authorities, doctors and healthcare professionals.
A refusal to reveal sexuality will also become part of the patient’s record.
But the news has angered many MPs and health campaigners who say the question is unnecessary and an invasion of privacy.
Tory MP Andrew Bridgen said: “I am very concerned about why this information is required. Under equality laws we’re all entitled to the same NHS and social care provision regardless of sexuality so why do they need to know it? And if people refuse to disclose it they will have a black mark on their record.”
Fellow Tory MP David Davies said: “The NHS should be trying to get people better not delving into their private life.”
The document, compiled jointly by NHS England and the LGBT (Lesbian, Gay, Bisexual, Transexual) Foundation, is entitled Sexual Orientation Monitoring.
An NHS England spokeswoman said: “All health bodies and local authorities with responsibility for adult social care are required under the Equality Act to ensure that no patient is discriminated against.”
A spokesman for Stonewall, which campaigns for gay rights, said: “We welcome efforts by NHS England and LGBT Foundation to improve the experience of lesbian, gay and bi patients. Monitoring sexual orientation can help GPs and other staff identify and recognise the unique health issues LGB people may face. Health services will be able to identify gaps in provision and areas for improvement.”
Countess Flavia Stampa Gruss, 80, a mother of two from Newport, was asked by a healthcare assistant if she was considering gender reassignment after a routine hospital procedure.
The Countess, who sits on a mental health board, said: “For heaven’s sake. Do you think I would get to this age and want that? What a waste of time and resources. Crazy.”