If you are sick you can fill in a self-certificate. which is available from the surgery, DSS or Post Office. A self certificate is for the first seven days of your illness. If your illness lasts more that one week you will need a doctors certificate. This can only be obtained via a face-to-face consultation with your doctor. Below is the link for a SC2 which will cover you for the first 5 days of your sickness.
www.gov.uk/government/publications/statutory-sick-pay-employees-statement-of-sickness-sc2