Whilst not that common, there are circumstances when an employee can be off sick from one job and receive sick pay, whilst continuing to work in a second job for another employer. Many employers automatically and, often incorrectly, refer to this as the employee 'defrauding' the company and even take disciplinary action, up to and including dismissal.
The legal position was clarified in the case of Perry v Imperial College Healthcare NHS Trust, which confirmed that as long as the employee is genuinely certified unfit to work and this affects their ability to carry out the specific job from which they are signed off, they are able to be off sick from it. In the meantime, if they are capable of performing another job, which is not affected by the reasons for being signed off sick, they can do so without any legal repercussions. The second job should not be undertaken during the hours of the job from which they are signed off, as the employee would then be paid twice for the same hours, which is not allowed.
For example, a worker has two jobs – a daytime job in an office and an evening job in a shop. They are signed off sick from the daytime job due to workplace stress as a result of heavy workload or bullying by colleagues. The stress prevents them from working in that specific job as the stressors are directly connected to it. That does not prevent them from continuing to work in the evening job, which is less stressful and is not affected by the reasons for being off sick from the other role.