Patients are responsible for self-certification for the first seven days of illness using the SC2 form available from the surgery your employer or on the Gov.uk Website.
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 of SSP (statutory sick pay).
A medical certificate, now called a statement of 'fitness to work' from your doctor is strong evidence that you are sick. If you have not been reviewed by the GP and this is the first time you require a note you may be requested to book an appointment with the GP.
Please note if you are requesting an additional medical certificate the GP can not complete this request till the other certificate has expired.
Statement of Fitness for work - 'Fit note'
The 'fit note' was introduced on 6th 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 Gov.uk Website