I’m a GP and a migraineur and I wouldn’t pay for a private scan OP.
It probably IS just migraine maybe worsening with perimenopause or stress or weather issues or similar, however if things are getting worse I understand why you might want a brain scan to be sure there is nothing new/serious going on. Sometimes it helps my patients to have that done so they can set that worry aside and focus properly on how we are going to manage their migraines, and me as well (though it’s maybe 95 percent for their and 5 percent for my reassurance!). Then we can both be sure nothing is being missed and avoid an unnecessary neurology referral.
Locally at least as a GP I can refer patients directly for a brain CT on the NHS (though sadly not MRI which avoids the radiation from CT). It may vary in different areas but worth asking your GP about this whole issue for sure.
There are downsides to a scan, high radiation for a CT, but as already mentioned any scan can find things you’d maybe rather not know about which might never cause you any problems and just create unnecessary worry… such as some benign tumours, odd cysts etc. Also things like brain aneurysms etc. which again may never cause you any bother but now you know about it you have to decide if you want to have brain surgery to prevent the possibility of them bursting etc.
It does sound like your GP doesn’t have a lot of knowledge about migraine management, it is unfortunately not generally that well taught to us as doctors (and if you haven’t experienced them yourself I think there is a general attitude of “it’s just a headache” just like the rest of society), and most of my own knowledge comes from being a migraineur myself and having done my own research with a background of having a medical degree. Sounds like you may need to explore preventative options. So ask reception to find out which GP is confident in migraine management and ask to see that GP. And if not getting anywhere ask for a neurology referral and/or use your money to see someone from the Migraine Trust privately rather than spending that money on a scan.
PS I personally use high dose aspirin to terminate a migraine and it works well and is in the guidelines! 600-900mg. I personally swear by Anadin Extra which also have a bit of caffeine and a small amount of paracetamol. Triptans work for me but leave ne feeling absolutely wiped out like I’ve had the flu for a week!