I have been restructured, and given a lovely new job description (according to HR and the union this is perfectly OK and legal).

Problem.

The workload is simply too great.

I have told my Head of Department that it is simply not possible for me to manage the proposed workload. My line manager has told the Head of Department the same thing. The rest of the team that I currently work with have told the Head of Department the same thing, however the Head of Department simply will not take it on board.

So, I have told the Director who is responsible for both our department and HR that this is an impossible workload. My line manager and the rest of the team have told him the same thing.

Ignored.

What do I do?
I am looking for another job out of sheer desperation, as the situation is making me ill, but suitable jobs are hard to come by.

Agree priorities with you line manager, do your best, go home when the bell rings. If you start getting written warnings about the lower priority things not being done then post again.

Have you told the union about the workload? Make sure you’ve got records of you telling your bosses it is too great, and their responses. That way, when a deadline is missed you can point to it. Don’t cave and work longer hours than you’re payed for.

Make your objections to workload on record recording all that everyone else has said

I owuld advise doing this in an informal style with an e-mail that says as you are aware x said the workload is too much as has y and also z

Explain you are willing to work hard are flexible adaptable love the company , highly skilled competent, trained etc but think it will end in failure

Assuming they dont deny it all then you have them admitting it.
Try to renegotiate a realistic role
If this fails then use this in evidence at any appraisal and try to negotiate a reduction in work load
Worst comes to the worst use all of that in a constructive dismissal claim

The main issue is at least you have a job whilst look for alternatives and the real issue is whether you think reality will make them re-evaluate the role or whether they will use this as a method of managing you out.

Dont actually try to do everything if it means loads of stress and failure just fail from the start but actually do your hours etc
That was my approach when asked to the impossible
IN a similar scenario I had weekly meeting with my director [ line manager agreed with me] to prioritise my workload as it was impossible [ and could be proved] to do what they wanted in the time allocated- we had a contract to deliver something that could not be done in the time allocated. As I did not negotiate the contract I said it was not my fault – this was accepted and “allowances” made but that was the end of any promotion opportunities from that moment onwards

Do what you can do, sod the rest.

are you allowed to give out the moderators motto on here?