It is normal for the Royal couple to be actively involved in their own planning, including the choice of suppliers
There is no protocol to dictate which wedding suppliers should be used, indeed dedicated wedding suppliers are unlikely to be Royal Warrant holders due to the conditions under which a Warrant is granted.
In the case of the wedding between Prince William and Kate Middleton, the Prince of Wales’s Press Office requested that we invite any businesses to contact the couple direct in the first instance, using the address we supplied at the time.
In order to apply for a Royal Warrant of Appointment a firm should have made a continuing supply of goods and services ordered and paid for by the Households of The Queen, The Duke of Edinburgh or The Prince of Wales over a minimum trading period of five years within the last seven, which should include trade within twelve months prior to the date of application.
In practical terms this rules out all dedicated wedding businesses; there simply aren’t enough weddings in the Royal Household to fulfill the requirement for a continuing supply of goods over a five year period.