I've been doing some reading on this.
Apparently if you start Utrogestan before day 15 of your ‘cycle', then breakthrough bleeding is common. The usual cycle using this regime is 15 days gel / patch / tablet then adding Utrogestan for 12 days from day 15. If breakthrough bleeding is a problem, then Utrogestan can be added at about Day 17 instead. If it's still a problem, then Utrogestan from day 19 for 10 days apparently.
I've just had a failed attempt at having a Mirena inserted (scar tissue from previous caesars) and had been bleeding every two weeks with Utrogestan. So, while I'm waiting for a gynae appointment to have the Mirena, a hysterectomy and d&c under general anaesthesia I've decided to stick with the Utrogestan and try one of the above methods xx