Under UK law if you are invited to attend a disciplinary or grievance meeting with your Employer you have the right to be accompanied at that meeting by a colleague or trade union representative, if you have one.
Other than these two, unless there is a provision in your Contract or Staff Handbook that says otherwise, you are not entitled to take anyone else.
You may also be surprised to know that you do not have the right to be accompanied by a legal representative, such as a Solicitor.
There are however a couple of important exceptions to this rule;
1) As set out above, there may be a contractual provision that allows for someone else to attend with you.
If you find yourself in the unfortunate position of being involved in a disciplinary or grievance procedure it is advisable to obtain a copy of your contract and any of the employer’s procedures, handbooks or policies at the earliest possible stage.
2) If you have a disability it may be a reasonable adjustment to allow you to be accompanied by someone else, which could be a lawyer.
Where an employee has a disability, in accordance with the Equality Act, an Employer has a duty to make reasonable adjustments to any arrangements that they make which place the employee at a substantial disadvantage in comparison with a person who is not disabled.
For example this could include allowing the employee to be accompanied.
3) You may be able to establish the right to be represented by a lawyer as a result of the Human Rights Act 1998.
The provision in question is Article 6 which is the right to a fair trial.
This will only apply however where the outcome of the disciplinary procedure would have a substantial influence on a regulatory body for a profession. For example a doctor who may find that he is struck off as a result of the disciplinary procedure would have the right to be legally represented at the meeting(s).
It is important to note that this is the legal position but the Employer has the discretion to allow you to be accompanied by someone other than a work colleague or trade union rep. Therefore there is no harm in asking the employer and perhaps giving them the name of the person, their relationship to you and details of why you want them to go with you.