You do not require a doctor's sickness certificate for any illness lasting seven days or less. Your employer may however require you to complete a self-certification form (SC2) which is available from your employer or on the HMRC website. If you want a medical certificate for a period less than five days this is not covered by the NHS and so will incur a charge.
Evidence that 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 of SSP (statutory sick pay).
A medical certificate, now called a 'Statement of Fitness for Work’ (see below) from your doctor is strong evidence that you are sick and would normally be accepted, unless there is evidence to prove otherwise.
You could also provide evidence from someone who is not a medical practitioner, e.g. a dentist. Your employer will decide whether or not this evidence is acceptable. If your employer has any doubts, they may still ask for a medical certificate from your GP.
To obtain a medical certificate you must see a doctor so please book an appointment or come to walk-in.
Evidence that your child is sick
The NHS does not provide sick note/medical certificates for children although we are happy to provide you with an appointment card as proof of attendance.
Statement of Fitness for Work - ’Fit Note'
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)