Getting married? You can apply up to three months early
You can apply in your married name up to three months before the ceremony. HM Passport Office holds the new passport and post-dates it to your wedding date.
This is worth planning around if you are honeymooning abroad, because your travel bookings and your passport need to carry the same name. Book flights in the name that will be in the passport you are actually travelling on. A mismatch between ticket and passport causes problems at check-in regardless of which name is legally yours.
If the honeymoon is soon and you have not started, start now. Three weeks guaranteed plus a three-month post-dating window is plenty of room. It is only plenty if you use it.

