Most employers dismiss staff 'reasonably' and with fairness. But, certain situations get classed as 'automatically' unfair reasons for dismissal.
Official 'Lawful' Industrial Action
An automatic unfair dismissal would occur if you fire someone for participating in lawful industrial action:
During a 12-week period from the start date of the industrial action.
After the 12-week period if you failed to take reasonable steps to solve a work dispute.
Note: Only a tribunal can determine whether you took reasonable steps to resolve the dispute.
You may decide to 'lock out' your employees for taking industrial action. Locking them out means you prevent them from accessing their usual workplace.
As a rule you can achieve a lock-out by locking the doors. But, you cannot include any days of the lock-out into the calculation of the 12-week protected period.
Automatically Unfair Reasons for Dismissal
Dismissal for a certain trade union related reason.
Dismissal for asserting a statutory right (e.g. objection to illegal deduction from wages or insisting on any of his statutory rights under the Employment Rights Act 1996).
Dismissal for asserting a right to apply for time off for study or training.
Dismissal because of a TUPE transfer or a reason connected with the transfer that is not an economic, technical or organisational reason entailing changes in the workforce.
All of the above qualify as an automatic unfair dismissal. In most of these cases an employee does not need to have a period of qualifying continuous employment except for:
Dismissal in connection with a TUPE transfer.
Dismissal because of a spent conviction.
Dismissal in connection with an application for flexible working. (But they will give rise to an automatic unfair dismissal if they are shown to be the reason for dismissal of someone qualified to claim).
Grounds for Automatic Unfair Dismissal in the United Kingdom