Capability dismissals generally fall into two categories: not capable by reason of ill-health and not capable because the employee doesn’t do their job to a reasonable standard.
Ill-health in this context typically means an employee’s long-term absence for medical reasons which places the employer in economic difficulty. Performance-related capability dismissals often occur after a prolonged period of under-performance.
Whether the employer is entitled to rely on capability as a fair reason for dismissal will depend on the circumstances of the case and each case tends to be fact-sensitive.
Redundancy is a little different. Redundancies occur most commonly where an employer has a reduced need for employees to do the work they were employed to do at the place they were employed to do it. This may be because of a loss of business, the introduction of new production techniques, a reorganisation or because the business is moving to a new location.
The decision to make redundancies is for the employer and the law won’t readily interfere in it.
For the most part, unfair dismissal claims relating to redundancy are about whether the employee who is made redundant, should have been selected for redundancy, not about the circumstances that led to redundancy.
It is frequently argued by employees that someone else should have been picked instead; or that the process followed by the employer to choose those made redundant was flawed; or that alternative work could have been made available to the employee, but wasn’t.
Redundancy is also different from other legally fair reasons for dismissal because it triggers a right to statutory compensation for those qualified to receive it. More information about statutory redundancy payments can be found here
Some other substantial reason is a ‘catch all’ term and includes things like a clash of personalities or failure to adapt to new working processes.