Those of us in the NHS know that this is not a solitary instance - long hours are the norm, most of us do more than our contracted hours. It's the culture of the organisation, you don't get it like this in industry (and I've worked in both).
I'm sorry it's turned out this way, evedawn, I know how much you were looking forward to the change.
These are in no particular order:
1. go to your Trust webitesite and look up the policy for flexible and part-time working.
2. Find your offer letter and contract which confirms your hours.
3. work out (quickly) what in your JD you can do in your 30 hours, and what will NOT get done if you have your scheduled 7.5 hours off each week. YOu have to prioritise so that you can explain why work won't be done if you only work your contracted hours, you will prioritise X and Y each week but you can't do everything, if they want it all done, they will have to cover you with someone else for the other 7.5 hours.
4. Look at the Trust policy on stress management (there will be one)
5. Suggest to your boss that if this keeps up, you will refer yourself to Occupational Health (as you are entitled to do) - incidentally you can just do that, you don't need to tell him you're doing it, and he doesn't have to refer you.
6, Are you being paid the overtime or being given time off in lieu to cover the extra hours? I bet you're not.
7. Talk to your department's HR manager asap in confidence
Is there too much work or not enough staff, or not enough skilled staff?
I know the feeling - I have been working more hours for longer than I care to admit, just to keep up, knowing that other people depend on my outputs - if I fall behind, people are directly affected by my not doing things.