A medical certificate should generally be accepted at face value as confirmation of a genuine illness, unless the employer has reasonable grounds for suspecting that your illness is not genuine.
If you take lots of short absences and your employer can show that this is significantly affecting the ability to organise work, your employer may be able to take action against you. They can do this even if your illness is genuine, and supported by a doctor’s note, or even if you are better by the time of the disciplinary action.
Your employer may ask for permission to approach your doctor, or ask you to see a doctor appointed by your employer for a report to be prepared on your condition. You need not consent, but if you don't agree, your employer will be entitled to make a decision about the impact of your health on your ability to do your job, on the basis of the information that it already has. This could lead to your dismissal.
Failing to cooperate with your employer’s request for a medical report may also affect any contractual rights you have to sick pay.
Before dismissal becomes an option, you and your employer must discuss ways of minimising the impact of your absence on the organisation and whether there are any ways to help you manage your health better.
You may be disabled. If your absences are because of a disability, you are protected from disability discrimination by the Equality Act 2010. This means that your employer must make any reasonable adjustments that could help you return to work. This could include more flexible working arrangements, part-time working, giving some of your duties to someone else, or moving you to a less strenuous post (all with your consent).
It would be disability discrimination to dismiss you because of a disability-related absence unless your employer can point to genuine and persuasive business reasons why it should not have to wait for you to recover. An employer will not be able to justify a decision to dismiss you in these circumstances unless there were no reasonable adjustments to be made (for example, changes in duties, working environment or hours) that could have helped you get back to work.
Before dismissing you, your employer must follow a proper procedure. In particular, you have the right to be accompanied to any formal meetings with your employer and to appeal against any decision.