As a worker, the law says that you have a legal right to be accompanied in disciplinary hearings by a trade union official or a fellow worker of your choice. If you choose a union official, this may be a person from any trade union, whether your employer recognises that union or not, and the person needs to be certified by a union as having experience in dealing with disciplinary cases. (Where you are a member of a union recognised by your employer, the person you may choose to accompany you is likely to be your current union representative.)
Your employer’s disciplinary procedure should explain your right to be accompanied and it may contain rights that are wider than the statutory minimum.
For example, the statutory procedure only entitles you to be accompanied to a disciplinary hearing, and not to any investigation meetings carried out to decide whether or not disciplinary action should be taken.
Especially in workplaces where a union is recognised, it is not unusual for a negotiated procedure to allow you to be represented by a trade union rep at the investigation meeting, as well as the disciplinary hearing.
Also note that if you have a disability, your employer has a legal obligation to make reasonable adjustments to the disciplinary procedure so that you are not disadvantaged, including allowing greater flexibility as to who can accompany you and when you have the right to be accompanied.
Whether a meeting is a disciplinary meeting or an investigation meeting depends on what happens at the meeting – not on what the employer calls it. Any meeting that is capable of resulting in some form of disciplinary sanction, such as a warning, will be a disciplinary meeting and you have the right to be accompanied.
It is always sensible to ask to be accompanied to the meeting by a companion, even if the meeting does not strictly qualify under the statutory right.