Do visualizations of giving birth in a happy healthy successful vbac, talk to baby and tell him/her it's time to come out and meet you, do relaxation sessions with deep breathing, do fear release writing in a journal - just write down all your fears each day to get them out. Acupuncture/chiropractic/massage. Up the sexual activities - long make out sessions, have him do nipple stimulation with his hands and mouth for at least 20 mins, or you can do it, may need to continue for hours to get steady labor going. Stress/anxiety/tension are your enemy- relaxation is crucial.
You can try this hypnosis track by Hypnobabies https://www.hypnobabies-store.com/All_MP3s-Come_OUT_Baby_MP3.html, not sure if it will work as well if you're not already doing the childbirth hypnosis program but it might be worth a shot! They also have 2 tracks for a successful VBAC. If nothing else they are excellent for relaxation.
Herbs - to ripen the cervix: (From Susun Weed's "Wise Woman Herbal for the Childbearing Year")
-Visualize cervix soft and thin.
-Evening Primrose Oil - 3 capsules daily for up to a week
-Black Cohosh tincture (sometimes called an extract) - 10 drops under the tongue hourly will have a noticeable effect on the cervix in three to four hours.
-Also semen as others have said.
To initiate labor (these will not work unless cervix is already ripe):
-Imagine your uterus contracting in a non-worrying way, don't force it or focus on the problem, just keep positive visualizations and feelings.
-Homeopathic Caulophyllum 200x, dose can be repeated every half hour for 2 hours.
-Stimulate the uterus by rubbing your belly softly and persistently with or without oil. Can use castor oil rubbed on the belly.
-Blue Cohosh tincture - 3-8 drops in a glass of warm water or tea, repeat every half hour for several hours until contractions are regular. If labor is not underway in 4 hours, use a dropperful of the tincture under the tongue every hour for up to four more hours or until contractions are strong and consistent.
-If tension or stress are a problem you can even smoke a little pot! Lol worked for my friend! One time won't hurt the baby.
-Laughter, good company, a glass of warm milk (calcium can help), a glass of wine, hot baths or showers, dancing, anything to help you relax and feel joyful.
You can order herbs and tinctures online through a reputable dealer like Mountain Rose Herbs (not sure what's available in the UK) - make sure they are organic and all natural. Good luck!