Gross misconduct in these circumstances would be very harsh and quite possible unfair. This would need to be something so serious that it justifies your instant dismissal. We are talking about theft from work, violence, serious negligence, placing the company into disrepute, etc. Not following a sickness procedure by simply not calling in is not really gross misconduct – it could be misconduct and you can be issued with a warning but to call it GM is somewhat unreasonable.
The issue in your position is that you are not protected against unfair dismissal. If you have been continuously employed at your place of work for less than 2 years then your you will not be protected against unfair dismissal. This means that your employer can dismiss you for more or less any reason, and without following a fair procedure, as long as their decision is not based on discriminatory grounds (i.e. because of gender, race, religion, age, a disability, sexual orientation, etc.) or because you were trying to assert any of your statutory rights (e.g. requesting maternity/paternity leave, etc.).
If the dismissal had nothing to do with any of the above exceptions then you would not be able to challenge it and your only protection would be if you were not paid your contractual notice period, because unless you were dismissed for gross misconduct, you would be entitled to receive your contractual notice period. If you did not have a written contract in place you would be entitled to the minimum statutory notice period of 1 week. Your employer would either have to allow you to work that notice period and pay you as normal, or they will have to pay you in lieu of notice.
There is a possibility you could try and argue your condition was a disability but you must be able to satisfy the legal test for disability. In the legal sense of the word, disability can have a broad meaning and there is no single list of medical conditions that qualify. Instead, to establish whether a person is disabled, they need to show that they meet the legal definition of a ‘disability’.
The Equality Act 2010 defines a disability as a “physical or mental impairment that has a substantial and long-term adverse effect on a person’s ability to carry out normal day-to-day activities”.
I will break this definition down:
- Physical or mental impairment – this can include nearly any medical condition;
- Substantial effect – the effect must be more than minor or trivial;
- Long-term - the effect of the impairment must either have lasted or be likely to last for at least 12 months;
- Normal day-to-day activities – these could include anything considered ‘normal’ in a person's normal daily routine (e.g. walking, driving, speaking, eating, washing, etc.)
If a person satisfies the above criteria, they will be classified as being disabled and will have automatic protection against discrimination, which means that they must not be treated unfavourably because of their disability. So if you believe that the reason for the dismissal was to do with this rather than your conduct, it could amount to discrimination.
You could instead try and discuss this with the employer and state that it is clear the relationship has broken down and that you will be parting ways but ask to do so in an amicable way, where you are just allowed to walk away and they do not tarnish your reputation with unreasonable allegations like GM.