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.
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).
It is up to your employer to decide whether you are incapable of work. 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.
Fit for Work Referrals
Fit for Work is a voluntary service that offers the wider working population access to occupational health advice and support. GPs and employers throughout England and Wales can refer their employed patients and employees who have been, or are likely to be, off sick from work for four weeks or more for a free voluntary occupational health assessment. The occupational health professional will identify obstacles preventing the employee from returning to work. A Return to Work Plan will be agreed providing recommendations tailored to the employee’s needs, which can replace the need for a fit note.
Fit for Work is here to support you in work, and if you’re off sick, in a way that’s right for you. Whether you work for yourself or an organisation, you can access expert and impartial advice delivered by the Fit for Work team of occupational health professionals. To chat online to a specialist advisor or speak to an advisor please visit http://fitforwork.org/employee/
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)