Hi Cathy
You've found the right place to be able to learn a LOT more about CH and how to deal with it. It's possible to get good treatment for CH here in NZ, however you need to be proactive to get it (just like anywhere else in the world). The problem is that CH is pretty rare, with most doctors having never seen anyone with it and very little, frequently outdate information to base treatment on.
Your current GP is certainly outdate with his treatment, which will be doing little to help Steve, other than giving him rebounds with the imigran tablets. You really need to work with a good neurologist, preferably one who specialises in headaches. You may need to see someone in Wellington as there might not be too many around the top of the South Island.
Verapamil is a good preventive with a good track record for preventing CHs, which is why it's the preventive of choice for most people. However 40mg 2-3x daily is a very low dose for CH prevention (it's more typical of it's use to lower blood pressure). Many people with CH need 360-480mg a day with some needing up to 1000mg (which will probably freak out your GP). Other preventives include lithium and topomax.
Verapamil can take 10-14 days before it is effective, so prednisione is normally used as a short term preventive, starting off with about 60-80mg a day, tapering off over about 10 days to nothing. By this time the verapamil should be working.
For aborting CHs, imigran (known as imitrex elsewhere) can work well, but it's the injectable form that works best for CH. It sounds like Steve has been using the tablet form that works, but takes about 30 minutes compared to about 5 minutes for the injections.
What works equally well is using oxygen via a non-rebreather mask at a high flow rate (at least 15lpm, with higher being better). I wrote about how I got oxygen in a series of posts you can read - Multimedia File Viewing and Clickable Links are available for Registered Members only!! You need to

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Using oxygen I can kill off a CH in about 6 minutes, which is a life changer.
Red Bull can help limit the intensity and duration of a CH, just chug a can as soon as a CH starts. However when using verapamil it's best to limit the use to 1-2 cans a day as the taurine in Red Bull acts in the same way as the verapamil (calcium channel antagonist), effectively increasing the dose.
Also try using vitamin D3 as a preventive too. It's getting good sucess - Multimedia File Viewing and Clickable Links are available for Registered Members only!! You need to

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I'm using it and I'm getting a lot less CHs now by a long way (in conjunction with verapamil).
Keep reading and ask questions galore. You'll soon know more than most doctors do.
Regards
Mike