I’ve looked to see what the 1992 Labour Relations (Consolidation) Act says and it is not clear to me what the answer to your question is. However ACAS have a guide and in that guide at page 3 it has a section Terminology.
It would appear from this para that ACAS clarify ‘trade union officer’ as a paid employee of the Union. Sorry to not be more help.
Have you asked your Union to clarify the legal definition and status of the person you refer to? They will have recourse to legal advice if not inhouse solicitors, but looks likely the answer is he/she is not ‘a Trade Union Officer’
Just a suggestion but I’d be re-checking the list of acceptable referees and be looking eleswhere?
http://m.acas.org.uk/media/pdf/k/k/Trad ... kplace.pdf
“Terminology
There are a variety of different terms used to describe a union representative. In law the term most often used is ‘trade union official’ but this can easily be confused with an official who is an employee of the union, otherwise known as a ‘trade union officer’ whereas ‘lay union officials’ are elected or appointed to represent members in a given workplace or location“
This is just my opinion, I’ve no legal training.