What does a union representative actually do?
Represents members in dealings with their employer — individually in disputes, and collectively in negotiation — with specific statutory rights that make the role more than informal support.
The individual role, which is what most members encounter:
Accompanying a worker at a disciplinary or grievance hearing. This is a statutory right — a worker may be accompanied by a trade union representative or a colleague, and the employer must permit it. The companion may address the hearing, put the worker's case, sum up and confer with them, though they may not answer questions on the worker's behalf.
Advising on rights and procedure, frequently the most valuable function, since procedure determines outcomes more than merits do.
Negotiating on individual issues before they become formal.
Referring to the union's legal service where a claim may exist.
The collective role:
Collective bargaining over pay, hours and conditions, where the union is recognised by the employer. Recognition may be voluntary or obtained through a statutory procedure where sufficient support is demonstrated.
Consultation on redundancies and on transfers of undertakings, where employers have legal duties to consult representatives.
Health and safety, where appointed safety representatives have distinct statutory rights to inspect, investigate and be consulted.
Learning representatives, with rights relating to training.
Their legal protections: reasonable paid time off for duties and training, and protection from detriment or dismissal for trade union activities. Dismissal for trade union membership or activities is automatically unfair, with no qualifying service required.
What representatives are not: lawyers, though many are highly experienced in employment procedure; and not able to compel an employer to agree.
Where there is no recognised union: you may still be a member and be accompanied by a representative, and in some situations elected employee representatives must be chosen for consultation purposes.
Joining after a problem arises is possible, and unions commonly apply a waiting period before providing representation on pre-existing matters — which is why joining before you need it is the practical advice.
General information, not legal advice.