Thank you very much for clarifying. If an employee has been continuously employed with their employer for at least 2 years they will be legally protected against unfair dismissal. This means that to fairly dismiss them the employer has to show that there was a potentially fair reason for dismissal and that a fair dismissal procedure was followed.
According to the Employment Rights Act 1996 there are five separate reasons that an employer could rely on to show that a dismissal was fair: conduct, capability, redundancy, illegality or some other substantial reason (SOSR).
Therefore, the first step is to establish which of these reasons is going to be used to justify the dismissal. Not only that, but they must also justify that it was appropriate and reasonable to use it in the circumstances.
Finally, they need to ensure that a fair dismissal procedure was followed and that the outcome was one that a reasonable employer would have come to in the circumstances. Each of the potentially fair reasons will have its own requirements in terms of the procedure that needs to be followed in order to make it fair.
What you have mentioned is unlikely to be able to justify instant dismissal for gross misconduct so you should really be considering a formal disciplinary, leading to an official written warning and only if further misconduct occurs should you be looking at dismissal in the future[VJ1] .
In terms of notice, if they are being dismissed for something very serious, which is gross misconduct, then no notice is due, but if it is not a gross misconduct dismissal, they would be due a week for each full year of service.