Used most the things you listed but my hair fell out, as a last ditch I finally tried one that wasn't from my GP as they never seemed to work.
After reading up on the internet, I bought the Philip Kingsley stuff.
I used it for a couple of weeks then around every three months for the last year and for the first time in ten years it's settled down.
I really thought, what with how bad it could get (scabs, hair loss etc) that a none prescription wouldn't work.
It does weigh your hair down, but when it washes out (I alternated with my normal stuff) it's really conditioning. I put the toner on my scalp in between washes if it's itchy, then it doesn't get out of hand, and it works instantly.
It's quite expensive (I think around £20 per bottle) but I've only bought one bottle of each and have only used about half in a year because it worked like magic and I went back to my generic shampoo.
I got the Philip Kingsley flaky/itchy scalps shampoo and the scalp toner for flaky/itchy scalps, there's also a scalp mask you can buy that's in individual treatments for a couple of quid, again
I bought them at John Lewis.
Sorry if that was a bit garbled, been up all night, hope it helps :)