Women on maternity leave who are made redundant still have the right to receive SMP (see the government website – direct.gov.co.uk under Employment/Work & Families/Pregnancy & Maternity Rights in the Workplace/Maternity Pay). You need to talk to your employer and they may need to contact the Inland Revenue to ensure that you continue to get your maternity leave payments.
Just on another point, I was not sure if you were aware that if a woman is selected for redundancy while on maternity leave, then special provisions apply to protect them. They must be given first refusal on any suitable alternative employment. It’s not clear from your email if the shop where you worked was one of a chain or not. If it is part of a chain and only certain shops are being closed, then by being on maternity leave, your employer would need to give you first choice of any jobs that become available at other stores.