I am worried about one of my employees coming into work whilst they are unwell. I know that flu cases are on the rise, as are other seasonal viruses that could make them and their colleagues very unwell. Am I able to ask all employees to wear a mask whilst at work to prevent the spread of illnesses?
The wearing of face masks of coverings as part of measures at work to prevent the spread of illnesses is down to you to decide; there is no law either preventing or requiring it, however you will need to be aware of any individuals with health needs that make this more difficult, or other reasons that relate to a protected characteristic that make this rule harder for them to adhere to. There may also be employees who have other good reasons for not wearing one.
Undertaking a risk assessment, perhaps similar to one completed for covid, will help you determine whether your working arrangements are such that may make face masks an advisable measure to prevent the spread of a contagious virus.
If you decided the wearing of a mask is required, you should communicate the reasons for your decision to your employees will help them understand why your rules are in place.