Op, ask for this to be moved to a busier board, maybe chat? Hopefully someone will see it there and advise.
I am not really sure but i always understood if you leave a job, you make yourself voluntarily unemployed and therefore no benefits are payable. I cannot offer any advice on that or benefits as, like you, have never claimed anything so really do not know but hopefully some one will know more. Also, your job is still technically available but the role requires longer hours in order to perform it ? Again, i have no personal experience but i have had friends that have come up against this over the yrs and they went back full hrs as they had no choice really. Could you afford the appropriate childcare if you returned?
Part time hrs will also need childcare provision unless you work eve's and yr DP is there to care for baby or vice versa daytimes.
I am not really sure what to advise. I worked full time with my first child as i had a mortgage etc so no choice really, my hands were tied. When i had my second , 6 yrs later, i was in a much stronger financial position with large equity in my home and actually handed my notice in when i was 6 mths pregnant as i knew i would not be returning. (I felt it better to allow them to fill that position permanently so that there would be no detriment to the business and my colleagues) . I remortgaged my property at that time and before i left, to provide me with an income for 2 yrs , equal to my yearly salary , over 2 yrs. I allocated myself my wage each month which i lived off and paid bills , mortgage etc and then returned to full time work again , when my youngest was 2.
You mention your DP is on a low income wage. With kindness OP, that would suggest to me that you do need to work, in some form, in order to contribute to family finances with a view to moving out of yr parents home in the fullness of time. Creating your own home and supporting your new family.
I suspect OP , if you voluntarily leave your role, once they have proved it cannot be performed on the hrs you have requested , you will not be entitled to much moving forward if you leave. We are also in exceptional times and the job market is flooded with people looking for work. Part times jobs are also part of that demand , from other parents with children. I am currently working full time but term-time only ( in a sch). I have been looking to reduce my hrs for well over a yr now and it is hard. The applicants per role is often in double and treble figures. My DC's are both grown up now so i have no childcare issues at all and i thought that would be a plus for me- no. The applicant pool is overcrowded with experienced mums like me. I work in a role where you need to be flexible and available for children and families at all hrs. I decided to change tact and return to commercial... part time commercial roles are even harder to find. I have worked in both sectors over the years.... applying for anything suitable ... am still looking 1 yr on , with no joy.
If i were in your situation OP i would spk to the CAB for specific advice about yr circumstance and then think carefully about the longer term , about your finances, your aims and ambitions for the future, housing, providing for your child, the family opportunities and freedoms your wage would provide etc.
I personally, in your position, would not leave one job , without another job in place.