Redundancy

Q Is it correct that I can’t make an employee who is on maternity leave redundant?
A You are able to make an employee on maternity leave redundant (or a pregnant employee still in work,) provided the reason for redundancy is not the employee’s pregnancy, or any other maternity-related reason, and provided the process is handled fairly and with transparency See Link.
You must ensure that any selection criteria are non-discriminatory and communicate and consult appropriately whilst they are absent on maternity leave. In addition, you must make every effort to find alternative employment including offering her another role before you offer it to anyone else. Discovery that an employee’s work can be managed by another employee, or that you are able to manage without that employee, will not be considered a valid excuse for redundancy.
In addition, any failure to could potentially result in an expensive employment tribunal. it is best to be sure this is the only option, and See Link.
If an employee is made redundant prior to going on maternity leave she will still be entitled to the full duration of statutory maternity pay (SMP), unless she was made redundant prior to the 15th week before the baby is due.

For more details on redundancy see here.