Please note that you are not required by law to provide a Fit to Work Note unless you have been off work for more than 7 days. If your employer wants one before this, then you will have to pay for a private sick note, and get your employer to reimburse you.
For sickness of 7 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.
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 DirectGov website (where this information was sourced)
If you have to be admitted to hospital and will need a note for your time as an in-patient, PLEASE ask the ward staff to issue you with one. The hospital doctor should also issue you with a certificate to cover you for the time that you are likely to be off work if you have had a major operation. You should not have to attend the surgery for this initial certificate.