https://www.maternityaction.org.uk/wp-content/uploads/Redundancy-2018.pdf
I would speak to ACAS as it might be that they have to honour you a role in an another dept. My sister in law has this. All of her dept were made redundant but she was offered another role because she is pregnant.
Everything will be explained in your first consultation meeting, 1st step is always notification and out laying the business reasons, then consultation, as your on mat leave you will be offered any suitable roles available over everyone else going through the process. I know it’s daunting and absolutely shit timing but please don’t panic, your hr team will support you through the process and you have more rights as a pregnant person. If there are no suitable roles available and you are made redundant you will be paid your entire maternity pay in one lump sum on top of any redundancy payments, accrued holiday and notice pay xx
Maternity Action have information which may be helpful. You're still entitled to SMP assuming you previously met the requirements to claim it