In certain circumstances, the probation period can be extended. Please see section 7:9 of the Probation Code of Practice [PDF 101KB].
If you are not enjoying your role you don't have to wait until the probhation period has ended if you would like to leave as long as you follow the notice period set out in your contact.
If a mentor has been appointed to assist you in the probation period, you may ask them to attend any of your probationary assessment meetings. If it seems that you are likely to fail probation, you have a right to be accompanied by another person of your choice at any hearing that is empowered to dismiss you.
For any further specific questions please contact your HR Business Partner.