Thank you. If you have been continuously employed at your place of work for less than 2 years then your employment rights will unfortunately be somewhat limited. Most importantly, 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.).
So if the procedures that they should be following are just contained in policies that are not part of your contract, it would be up to the employer to decide whether to follow them or not and they can dismiss you for no apparent reason and without any fair procedure in place. However, if the procedures are part of your contract of employment they would be expected to follow them because if they do not they can be guilty of wrongful dismissal, which is a dismissal in breach of contract.
As to being signed off sick, it is possible for them to still go ahead with the hearing even if you are off sick. The failure to postpone the meeting would potentially make the dismissal unfair but as you are not protected against that they can go ahead and do it regardless.
I hope this has answered your query. I would be grateful if you could please take a second to leave a positive rating (3, 4 or 5 stars) as that is an important part of our process and recognises the time I have spent assisting you. If you need me to clarify anything before you go - please get back to me on here and I will assist further as best as I can. Thank you