Your GP will be the person responsible for supplying you with your sick certificate. If you are employed, to qualify for sickness benefit you will need to give this note to your employer. If you are unemployed, then you will need to send this to your Jobcentre Plus or to the DWP.
If you are concerned about your illness being disclosed to your employer or other colleagues at work, you may wish to consider what is recorded on this certificate. It is worth considering that a number of different people may see the certificate at your place of employment. If you have any concerns you should discuss them with your GP. Explain to them why you are concerned, with a view to negotiating a more acceptable term. It may, for example, be possible to explain your absence from work simply by describing a specific symptom like exhaustion, depression or inflammation of the liver. Remember that your doctor has a legal obligation to accurately record the reason why you are unfit for work, but there is always some flexibility here. Be aware though, that your doctor is unlikely to make a false recording.
Sometimes your specialist or clinical nurse specialist will be able to provide your employer with additional information supporting your absence from work. This additional information could include confirmation regarding the frequency of hospital visits, symptoms and side effects of treatment. It is not necessary for your employer to know what treatment you are taking or what condition it is for. If you wish your specialist or clinical nurse specialist to supply this additional information and you are at all concerned about the content of the letter, then be sure to let them know you want to view the contents prior to it being sent.