I would love to you fight this, as he should not be getting away with this.
As has been said, his ass in not covered, it sounds like he has made a judgement that the pregnant women he employs do not have the energy for the fight and can be easily bought off.
If you dont feel you can fight it, then be careful about what you do, to ensure you get the state maternity benefit. You must be in a job the day you start maternity leave, or you get nothing. It is designed to replace income. If you have no income to be replaced, you get nothing.
You can take maternity benefit from 24 weeks, but you need to apply in advance and get your employer to fill in part of the form, so it will be too late to apply if you get offered redundancy, take it, and apply for benefit the first day that you are off work. Apply while you are in employment.
If you are offered redundancy, insist that the benefit application is made out before anything else happens.
What ever happens, good luck and make sure that your boss knows that you know your rights.