Probably the first thing that I would do is resign from whatever representative position I held. If as a rep, I was instructed by the union, TUC and ACAS that this was the best deal on offer and I disagreed, then my position would be untenable. I am and always will be an employee first.
The more I learn on what business can and can't do to you, the more I realise that you need to have a good relationship with your employer, because if not, you are buggered.