@Minty
Sorry to hear you're struggling with this, although it might explain 04:30 appearances on GMEB threads!
The best advice, I've encountered, is to break the mental association between being in bed and unable to sleep. Use the bedroom for sleep (and pleasure!) only. All TV, books, laptop/mobile activity is to be banned. If you cannot sleep, get out of bed, put on something warm, go downstairs and do some activity until you feel tired enough to drop off as soon as you lie down.
Meanwhile, in daytime, increase the distances you walk and exercise in general (under GP advisement!), since this will help tire you out.
My problem isn't insomnia, per se, but it does start with that inability to switch off. I can be up to 6am but, then, I'm sleeping in the daytime, leading to up to a fortnight "out of phase" with the real world, awake at nighttime, unable to get to shops, attend GP appointments, exercise, do chores etc. I don't have a name for this yet.