Unions are the scourge of modern day Britain, Thankfully Maggie destroyed all but the last few percent of them,
In all my years, I have never once seen a union or their reps doing an ounce of good,
I have sat and watched them play barrister in disciplinary meetings were an employee is bang to rights, then come out and have a laugh with me about his chances etc.
they epitomise the idea of Champagne Socialism, the 'working man' living off the back of the real working men's union contributions.
the best thing to happen in the last 5 years with unions was the death of that Bigot Bob Crowe,
and the answer to your question is no, they can do nothing about anything, all they can do is protest over petty incidents to justify their wage.
as for not representing you properly at a disciplinary, after you have crossed a picket line, says it all really, pure bias against a 'greater' cause, regardless of your individual feelings on that situation.