I have been with my current employer for the last 3 years and i found out in November i am pregnant (i am currently 21 weeks). I have suffered with prenatal depression and my employer is not at all supportive, to the point i no longer want to work for the company! I have seen my dream job advertised and really want to apply BUT i have no idea where i would stand with maternity pay if i were to leave my current employer and take a new job.
You would not be entitled to maternity pay with your new employer. You could still get SMP from your current employer even if you resign - see here Bear in mind that you would then be unemployed though!