If you have a medical cause of absence from work for 7 days or less, you do not require a Fit Note (MED3 or "sick certificate"). You can complete a Self-Certification form yourself. If your employer insists on a medical note or assessment, this should be provided by your employer's occupational health department/contractor. In exceptional circumstances we may be able to provide a letter. This typically involves a charge of £10.
For further information on Fit Notes and self-certification, please visit the NHS website