Thanks for your patience. To be able to dismiss you immediately the employer has to show that there was an offence amounting to gross misconduct. As you have more than 2 years’ service you are protected against unfair dismissal so the employer will have to show that there was a fair reason for dismissal and also that they had followed a fair procedure.
What makes smoking a gross misconduct offence will depend on various factors. For example, was there a clearly communicated policy which said that smoking is prohibited in no-smoking areas and that doing so would amount to gross misconduct? Would smoking where you did expose others to risk or affect the image of the company, such as if you seen by customer, suppliers, clients, etc?
There has been case law which has ruled that smoking in non designated areas, even if it was a one off offence, can amount to a fair dismissal. You can read about this here:
It does not automatically mean it can amount to dismissal but if there was a clear policy which said that breach of the smoking rules can amount to dismissal then it can happen. On the other hand if there was no policy in place which designated the non smoking areas the dismissal could be deemed harsh.
This is your basic legal position. I have more detailed advice for you in terms of the options you have on taking he matter further if you are dismissed, which I wish to discuss so please take a second to leave a positive rating for the service so far (by selecting 3, 4 or 5 stars) and I can continue with that and answer any further questions you may have. Don’t worry, there is no extra cost and leaving a rating will not close the question and we can continue this discussion. Thank you