Is it lawful for an employer to ask a candidate if he or she has any criminal convictions?

An employer can ask questions about convictions in general, but in most cases, because the right to conceal a spent conviction is a statutory right, employers may not refuse to employ someone who conceals any convictions that are spent. If applying for a job in certain job categories, for example posts involving regulated activity with children or vulnerable adults, a job applicant must disclose all convictions, whether or not they are spent (see Quick reference > Jobs where it is lawful to ask for details of spent convictions). It is the duty of the employer to explain to the job applicant that the job falls into one of the excluded categories and advise him or her that disclosure of any spent convictions is required.