That's not true, as far as I know (and only because I looked this up when I worried about it). You get up to and including 7 days and you shouldn't have to give a note. From gov.uk[0]:
>If employees are off work for 7 days or less, they do not need to give their employer a fit note or other proof of sickness from a medical professional.
>When they return to work, their employer can ask them to confirm they’ve been off sick. This is called ‘self-certification’. The employer and employee will agree on how the employee should do this. They might need to fill in a form or send details of their sick leave by email.
>If employees are off work for 7 days or less, they do not need to give their employer a fit note or other proof of sickness from a medical professional.
>When they return to work, their employer can ask them to confirm they’ve been off sick. This is called ‘self-certification’. The employer and employee will agree on how the employee should do this. They might need to fill in a form or send details of their sick leave by email.
[0] https://www.gov.uk/taking-sick-leave