You must meet the following three conditions in order to get SMP:
To receive SMP you must give your employer 28 days’ notice of the date that you want the pay to start on and you cannot change your mind about this date.
Your SMP can start on any day of the week that you choose and in most cases will start on the same day as your maternity leave period starts.
To claim your SMP, you must give your employer a copy of your MAT B1 form – your maternity certificate which states your expected week of childbirth which your midwife or GP will give you when you are about 20 weeks pregnant. You may find it easier to give your notice for your leave and pay together in the 15th week before the baby is due. However, if you decide to do this you must remember that you cannot change the date that your pay starts on, even if you decide to vary the date that your leave begins on.