A wedding blessing as it is commonly known follows the legal marriage in either a Registry Office or church
A Blessing with a celebrant can be  part religious, spiritual or non religious in  nature,  and in essence, the wedding (blessing) ceremony is every bit the same as a full traditonal wedding ceremony where couples stand together to proclaim their love, exchange vows and rings in front of their loved ones, family and friends.
Some couples also choose to invite family members or friends to say a blessing or a prayer to participate in their special day.
Legalisation of your wedding.
As it stands today, it is only Registrars and designated Clergy and Marriage Officiants who are able to perform and complete and formalise the appropriate legal marriage documents.
However this can be done in a Registry office a day or two before  or even afterwards - or when convenient to you - as it is your choice when to legalise your union and there is no need to exchange wedding rings at that point or invite family and friends (apart from the standard two witnesses)
You are then ready to enjoy your unique and special wedding celebration ceremony in front your family and friends who need not know about the previous  or subsequent registry office trip.
Most guests at weddings are not aware of any differences as there will also be - if you wish -
a signing of the certificate (commemorative of the day) alongside your witnesses and wedding celebrant.
In order to arrange the legal aspects of your marriage (in addition to employing a Celebrant).
Give notice of marriage at your local Register Office at a cost of 33.50 each
An authority for the marriage is issued by the Superintendant Registrar, and you are free to get married in any district by submitting your completed marriage notice forms to the Registrar of Marriages in the area of your choice for marriage.
Arrange a trip to  The Registry Office to legalise the marriage which will take approximately 10-15 minutes and you will repeat a legal declaration and sign the Marriage Register in front of your two witnesses
Currently Registry Office = 40 and an extra 3.50 for  one wedding certificate.
Total Registry office and legalisation costs currently just over 110 (costs subject to change).

Blessings