Will I be legally married if I have a Celebrant ?

No, you must  register your marriage at the Registry Office by undertaking a marriage service.  All Local Authorities provide a "no frills" service which is often no more than 10 minutes and is quite a cheap option. You can go in jeans, if you wish, with a couple of witnesses.  Then dress in all your finery for the big day - your Wedding Ceremony.

The advantage of this is that you are then free to have the wedding of your dreams without the limitations imposed by the rules relating to a ceremony led by a Registrar.  

You can hold your ceremony anywhere and do not need to use premises which have been approved for weddings.  So whatever your dreams for your special day you can be sure you won't have to compromise.