Although disciplinary and grievance procedures at work are covered by the ACAS Code of Practice, employers don’t have to follow the code. This means you could get fired if someone makes a false allegation against you, if your boss believed the allegation and felt it was serious enough to warrant dismissal. However, this should not happen and you would have legal redress.
If false allegations are made against you, you may initially be unaware of it. Moves could be taking place in the background, on the part of your employer, to remove you from your post. However, legally, an employer cannot fire you for something you have not done. The problem is that some allegations, such as allegations of physical abuse, are so serious, that often an employer will choose to suspend you on full pay pending further investigations.
Having your say
If your employer follows a fair disciplinary procedure, at an early stage in the process, you should be given a chance to tell your side of the story at a disciplinary meeting. If you are in a union, you can ask your union official to advise you and accompany you to the meeting. Explain yourself honestly and accurately at the meeting, answering specific accusations calmly and truthfully. You should have nothing to fear if the allegations are false.
Bear in mind that the false allegations may have been made erroneously, or in good faith, by someone believing you to be the perpetrator of a serious misdemeanour or even a crime. People who make allegations can do so under certain circumstances with a conditional legal defence called "common law qualified privilege." The law protects complainants so long as their allegations are not malicious, and are made for reasons of legal or moral duty.
False allegations made by you
You could be fired for making false allegations against a colleague. It depends on the type of allegations you make. If you allege a colleague has committed a serious offence knowing this in not true, the ripple effect might cause damage both to the individual and to the organisation. Few bosses will tolerate the upset and upheaval likely to be caused by this kind of act. It would probably be termed "gross misconduct" and be grounds for dismissal following a disciplinary meeting.