Without commenting on the various "opinions" on the rights and statutory procedures for representation, I would suggest that anyone with any queries first of all reads the ACAS booklet on disciplinary and grievance procedures, available for download at :
http://www.acas.org.uk/CHttpHandler.ashx?id=272&p=0
Note the right to "accompany" by either a TU official or workplace companion, and the rights to paid leave for a workplace colleague to research and prepare. There is no requirement for a nominated TU official to come from a "recognised" union.
Presumably, if the PCCC wished to take on this sort of role, and they weren't a trade union, they could still provide workplace colleagues as part of their membership services.
Although ACAS Code of Practice advice has no statutory effect, in reality Employment Tribunals use them as their "bibles" and woebetide any employer that develops any alternative procedures that weaken the individual's position. The majority of successful unfair dismissal claims are because an employer fails to follow procedures from the ACAS guidelines.
The ACAS website also contains a vast amount of information about the application of legislative rules in the UK workplace. ACAS regional offices will always provide free impartial procedural advice to any employee subject to disciplinary process.
The one good thing of being represented by a "Full time" union official (not a rep), is that they may spend a great deal of their time doing just that, and are therefore tend to be much more procedurally aware than atypical employer middle manager.