Please help with my maternity leave >career break> flexible working situ!

[Wearegoingtobedlehem]

I am currently on career break following maternity leave.
I am absolutely aware that the only things guaranteed are my wage and contracted hours (ft).
The problem arises whereby I need to reduce my hours, as I just don't have the childcare available for 5 full days. I think I have been reasonable, asking to reduce with a pretty broad variance on number of hours I would like and the hours that I can work them.
They can't fit in with this, so I am concerned that I will be forced to return full time.
Meanwhile I have found what seems to be the perfect part time job with a different trust, the hours work.
How do I stand applying in this situation do you think, with regards to my current employer?
I have spoken with the potential new job, they have no issue but admittedly obv could not advise on the hr aspect.
Sorry for the ramble, I just can't go back full time or 7.5 hr days.

I don't see this situation as any different from looking for any new job while you are employed elsewhere.
You are free to apply for any job you want. If you do get offered a preferred job, you will then give your current job the required notice (and potentially might have to work a notice period). If you did get the other job, you could also use it as a bargaining tool at your current job (if you'd prefer to stay there).

The other thing to consider if whether you have received any maternity benefits e.g. enhanced maternity pay that might be affected by your not returning to your original job.