Yes. Sections 11 and 12 of the Employment Act 1989 as amended by Section 6 of the Deregulation Act 2015 exempts turban-wearing Sikhs from any legal requirement to wear head protection at a workplace. A workplace is defined broadly and means any place where work is undertaken including any private dwelling, vehicle, aircraft, installation or moveable structure (including construction sites).
There is a limited exception for particularly dangerous and hazardous tasks performed by individuals working in occupations which involve providing an urgent response to an emergency where a risk assessment has identified that head protection is essential for the protection of the individual eg such as a fire fighter entering a burning building, dealing with hazardous materials.
The exemption applies only to head protection and Sikhs are required to wear all other necessary personal protective equipment required under the Personal Protective Equipment Regulations 1992. The exemption does not differentiate between employees and other turban-wearing Sikhs that may be in the workplace, eg visitors. However, it applies solely to members of the Sikh religion and only those Sikhs that wear a turban.
Employers are still required to take all necessary actions to avoid injury from falling objects by putting in place such safe systems of work, control measures and engineering solutions eg restricting access to areas where this may be an issue. Where a turban-wearing Sikh chooses not to wear the head protection provided, the exemption includes a limitation on the liability of the duty-holder should an incident occur.
Article source: http://www.hse.gov.uk/contact/faqs/sikhs-head-protection.htm