An employer can ask a prospective employee to complete a medical questionnaire, but only after it has made them a job offer and only if it complies with data protection requirements. Section 60(1) of the Equality Act 2010 prohibits employers from asking job applicants questions about their health before offering them employment (with some exceptions).
If an employer intends to ask prospective employees to complete a medical questionnaire after making them an offer of employment, it must ensure that it has a legal basis to do so under the UK General Data Protection Regulations, as any information received will amount to processing their personal data. The employer would have a legal basis if processing is necessary to establish an employee’s fitness to do the particular work and to comply with health and safety obligations.
We would suggest that when making an offer of employment, you make the offer subject to you receiving satisfactory references, the right to work in the UK and receiving a satisfactory pre-employment health assessment. Then, if you do receive any information after the employee has started that doesn’t meet your definitions of satisfactory, with professional advice, you may be able to terminate employment.
We would suggest that you outsource the pre-employment health assessment to a service to a reputable Occupational Health Provider such as one of the partners we work with Flex OH; https://www.flexoh.co.uk/about-us