Evidence you are sick
If you are sick for more than seven days, your employer can ask you to give them some form of medical evidence to support payment.
Your employer can ask you to confirm that you've been ill. You can do this by filling in a form yourself when you return to work (self-certification). You can obtain these forms on the HMRC website or from the practice.
If you are off work for more than seven days, your employer may ask for proof of your illness. Most employers ask for a sick certificate from your GP.
However, this will also depend on your employer's company policy on sick leave. This policy should tell you how many days you can be off sick before you need to provide proof of illness.
You could also provide evidence from someone who is not a medical practitioner e.g. a dentist. Your employer will decide whether this is acceptable.
Statement of Fitness for work
The 'fit note' was introduced on 6 April 2010. With your employer's support, the note will help you return to work sooner by providing more information about the effects of your illness or injury.
For more information see the DirectGov website (where this information was sourced)/