Traditionally, invitations to private functions were addressed solely to the wife. If an invitation was to a public function, it was conventionally addressed to the husband and sent to his official address.
These old-fashioned customs reflect a long-vanished age, when
wives were firmly in charge of the domestic sphere, and husbands
went out into the professional world to work.
Today, it expected that social invitations will be sent to both the husband and wife for both private and public functions.
Traditionally, a husband and wife were addressed as follows:
Mr and Mrs John Debrett
However, many wives today do not like feeling subsumed into the husband's forename, and may opt for the following forms:
Mr and Mrs Debrett
John and Mary Debrett
In an official capacity, the person who is the prime invitee (be it husband or wife) will be the 'lead' invitee, as follows:
The Reverend John and Mrs Smith
The Worshipful Mayor of Worcester and Mr Brian Allington