It may be worth reading this..
Dismissals due to illness
Sometimes an employee may have to stop working because of long-term ill health. They may resign, or you may have to consider dismissing them.
Considering dismissing an employee
Dismissal is a last resort and you should consider as many ways as possible to help the employee back to work, including:
getting a medical report from their GP with the employee’s permission - they have the right to see the report before you do
arranging an occupational health assessment
work out whether or not they’re disabled and make any reasonable adjustments to help them do their job
If the employee cannot do their job because there are no reasonable adjustments that can be made, it may be fair for you to dismiss them, even if they’re disabled.