What happens if someone is asked to restrict their duties but, despite acknowledging the risks to their health involved, they say that they want to continue to work on the front line?

As their employer, you have an overriding duty to provide a safe system of work. The Trust would not be able to run a defence to say that an employee “waived their rights” and chose to continue to work. Provided the decision around restricting duties has been carefully thought out, a full risk assessment undertaken and the employee has been truly consulted about the impact on them, then the decision taken will be a reasonable management instruction. Failing to follow that reasonable management instruction could amount to a disciplinary offence.