You should be entitled to Statutory Maternity Pay from your employer, otherwise Maternity Allowance from DWP.
If you have a mortgage you can apply for Mortgage Interest Relief by applying for Income Support. You may also be entitled to Income Support depending on your circumstances. If the mortgage is in joint names your partner should make arrangements with you to deal with the mortgage payments.
For Council Tax you should qualify for single person discount and you should be eligible for Council Tax Benefit.
When the child is born you should be entitled to claim maintenance for the child from your partner.
The DWP booklet
A Guide for Lone Parents covers the main benefits. You should be able to pick up a copy from your local jobcentre.
If there are any issues over separation it might be best to make an appointment with your local CAB.
Hope the little one arrives safely.