What makes an interview question illegal in the UK
Under the Equality Act 2010, it is unlawful to discriminate against job applicants on the basis of nine protected characteristics: age, disability, gender reassignment, marriage and civil partnership, pregnancy and maternity, race, religion or belief, sex, and sexual orientation. An interview question is discriminatory if it could be used to make a decision on the basis of one of these characteristics — even if the interviewer has no discriminatory intent. Not every inappropriate question is illegal, but many commonly asked questions cross into unlawful territory.
Common unlawful questions: "Do you have (or plan to have) children?" (pregnancy/maternity/sex). "What religion are you?" (religion or belief). "Are you married?" (marriage and civil partnership). "How old are you?" or "When did you graduate?" (age). "Do you have any health conditions or disabilities?" (disability — unless it is a necessary occupational requirement). "Where are you originally from?" (race). "What does your husband think about you travelling for this role?" (sex and marriage).
How to respond in the moment
You have several options when an illegal question is asked, and the right one depends on how much you want the job and how egregious the question was. Option 1: Answer anyway. If the question is mildly inappropriate (e.g., asking your age) and you are comfortable sharing the answer, you can simply respond and move on. You have not waived your right to a complaint later. Option 2: Redirect to the underlying concern. "I think what you might be asking is whether I can commit to the travel requirements of this role — I can, absolutely." This is the most tactically useful response: it disarms the question by addressing the legitimate concern behind it without answering the unlawful question. Option 3: Politely decline to answer. "I prefer not to discuss that. I am happy to confirm that [the professional competency you imagine they are concerned about] is not an issue for me." Professional, non-confrontational, and protects you. Option 4: Address the question directly. "I am not sure that question is one you are allowed to ask. Is there something about the role requirements I can address instead?" This is appropriate if the question is egregious or part of a pattern and you are less concerned about preserving the relationship.
What to do after the interview
If you believe you were discriminated against — you were asked illegal questions and you did not receive an offer, and you believe the questions influenced the decision — you have the right to make a claim to an Employment Tribunal. The time limit is three months minus one day from the date of the act of discrimination. Before a tribunal claim, you can submit a questionnaire to the employer asking them to explain their decision. ACAS early conciliation is required before a tribunal claim. In practice, pursuing discrimination claims for interview rejections is difficult: proving the causal link between the question and the decision requires evidence. Document everything: dates, questions asked, what you said, who was present. If you have a pattern of discriminatory questions across multiple interviews, the documentation becomes more useful.
Legitimate questions employers can ask
Employers can ask: whether you have the right to work in the UK (this is a legal requirement to verify). Whether you can perform the specific essential functions of the role (for disability-related questions, this must be framed specifically: "Are there any reasonable adjustments we would need to make for you to perform this role?" not "Do you have any health conditions?"). Whether you are available on specific days or times (work pattern requirements), without asking why you might not be. Whether you hold specific professional qualifications, licences, or registrations required for the role. Understanding the boundary helps you identify when a question has crossed it.