Everyone has given good advice. If you are in a union do speak to them.
I don't think you should have to raise a grievance to resolve this, but you might have to. Plus if you end up taking this further at any point, you will need to have raised a grievance first, so it's not a bad idea to do so.
I agree with smittenkitten about approaching senior HR person and saying you want to resolve situation without resorting to grievance, but give them a short timescale for this, and be prepared to raise a grievance. It's not that hard, you would just need to do a letter saying what you've said to us to the right person. It might be stressful, but it's stressful already.
Probation doesn't have any meaning in law, it's just a tool used by employers to manage new employees. That's why you need to clear this up. But don't worry, the fact that your manager has said you are on 'probation' doesn't affect your employment rights at all. You need to clarify what this all means, and what the terms of your 'probation' in this new job are, and be prepared to raise a grievance, about this, and about any concerns raised about your performance without specifics or without you being given an opportunity to address them.
Must run, hope that helps a bit, good luck.