Variance of contract shambles

[Typhoon38]

I'm after some advice as I MIGHT potentially have to resign from a job then sue the employer for constructive dismissal. Please bear with me, it's quite a long story ! I work in the Public Sector and have been in my present post for 2 years. Recently, the organisation decided that a new shift pattern was required which involved cutting us from 5 rotas to 4, working 12 hour days / nights on a 4 on 4 off pattern. This was not a choice on our part, we were told (??) that we didn't like our current pattern and we all 'wanted' the 12 hour one....We are due to start that pattern in May.
In my role there are 3 bases at which I can work, but my PERMANENT base is local to me, 10 minutes drive. The other 2 bases are each around 40 minutes drive away, one West, one East. My initial contract states that I can be "required to serve at" any of the three and I do sometimes have to travel for the odd shift to cover leave, sickness etc. What it DIDN'T state, or so I thought, was that I could be PERMANENTLY moved to one of the other places of work...that was until a couple of weeks back....
The job are saying that we are 2 people 'over strength' at my place of work so 2 people have to move West on a permanent basis, even though this actually puts two rotas OVER strength at that location ! Two people were selected based on what I think is a flimsy, discriminatory post code lottery i.e. whoever lives closest to the other place, even though it's still 40 minutes away and even if it's by a few hundred yards, gets told to go. Until last week I was NOT one of those chosen and I received my variance of contract re my new shifts which clearly states I am based at my usual, i.e. local, base. The rota I am being placed on matches my Wife's shift pattern as she is already on the 4 on 4 off shifts, this was agreed to in writing by the people making all the changes and by my management team.
Within 2 days of receiving and signing this variance, my employer is now saying that one of the two 'movers' was only moved as a 'paper exercise' as he was on long term restricted duties...he now says he's coming back full time in June and he lives about 800 yards further east than me...so guess what ? The managers are now suggesting I might have to move instead. Not only is this going to add nearly 90 minutes onto my 12 hour shifts but if they move me onto the rota the other chap was meant to be moving to, I will be on totally opposite shifts to my Wife, no days off together, end of work-life balance.
So, I have penned them a very long email explaining several reasons why I can't entertain this move, and am awaiting a response. I am not hopeful.
If they insist on this move, I feel I will have to resign but am absolutely fuming at the shambolic way in which this whole matter has been dealt with. If I end up resigning, I intend to sue them for constructive dismissal, through my union and hopefully with advice from ACAS, as they have created a hostile working environment for me and prevented me from continuing in a job I enjoy, am physically and mentally able to do and one I like to think I am fairly good at.
Sorry for the long thread as a newbie....any advice / thoughts would be welcomed ! Ta

[ULA]

This is all about your employer changing your terms and conditions of employment. Firstly, is there a clause in your contract allowing for the company to make changes to your shift pattern? In regard to location it would appear from the brief exert of the clause you posted that your employer can require you to work at any of the three locations. The full clause would be helpful in order to confirm my view.

Depending on your answers to the above, in order to implement a significant change in your terms and conditions and if there is nothing in the contract that allows them to do so, your employer needs to follow a fair process. So, they need to fully consult with you and try to agree any changes, if they do not want to face a claim for breach of contract.

If you do not agree the law does recognise that employers have to adapt to changing market conditions, and that sometimes the contract of employment must be varied to reflect this.

You have quite rightly written to your employer in regard to the effect on your personal circumstance regarding the proposed changes and they need to give reasonable and due consideration to these and any alternative suggestions that you put forward. However, they do not necessarily need to agree to them if they feel they are unworkable. In which case they can terminate your original contract and offer a new one in its place on the new terms.

If you do not agree to the changes, then you must make it clear to your employer. You should do this in writing, sign and date your letter, and keep a copy. This letter will count as a written grievance.

If you don’t tell your employer you disagree with a change, this will be taken to mean that you’ve accepted it.

You should do this straight away, or as soon as possible after the change has been introduced.