Following my period of paid maternity leave, must I then take my entitlement to unpaid maternity leave?

No.  You may take as much, or as little of your unpaid entitlement as you wish.  Alternatively, you may choose not to take any unpaid leave following your paid maternity leave.

The only stipulation is that you must take a minimum of 2 weeks’ Compulsory Maternity Leave immediately after the date of childbirth.