Class 4 NIC on Dentist Materntiy Pay

Not come across this one before. Client is self-employed dental associate and has received NHS maternity pay (and had superannuation deducted). Happy that the gross pay is taxable, and then claim superannuation, BUT is it subject to Class 4 NIC? I am assuming that it is, as SMP paid to an employee would be subject to NIC, but just want to double chheck as the total involved is substantial (five figure sum).

Thank you