Hey man, don't lose hope. It's more difficult now and they've tightened the restrictions on getting benzos prescribed here, but it's still a far cry from impossible. The first thing is your choice of GP. I too have been in doctors offices where they have signs on the wall in the reception/waiting room saying "We do not prescribe benzodiazepines here", but that's not the policy for every surgery, just certain specific ones. If your GP's office has that policy or even your psychiatrist then the beauty of our system is that we are free to change GP/psychiatrist as we wish. Under the laws governing the NHS any patient is free at any time to change GP and request a new psychiatrist without giving any reason as many times as you want. Don't take the psych nurse's word for it, give the psychiatrist a try first, but if it's a no-go then just leave and find a new one. If you've had similar lack of luck at the GP then change them too. Don't assume because one doctor or one surgery won't do it that none of then will. It's entirely down to the discretion of that particular doctor, so all you have to do is find one who's a little more liberal/empathetic. If you aren't already, ensure you aren't mentioning benzos by name since that's the easiest way to ensure you walk out empty handed with a regular GP.
It's possible to give an excuse for why you can't take their first suggestion - for example, if they prescribe SSRIs tell them that you tried them before and not only did they not work but you had severe sexual side effects and migraines (its best to give the "cant tolerate" excuse on SSRIs since they will expect you to try them for up to 6 weeks before you can move onto a different drug and get closer to benzos), but if you rattle off a bunch of excuses for every medication the GP mentions then they're going to get suspicious - e.g. "Hmm, maybe we could try you on fluoexetine?" "Oh no doc, I tried those before and they didn't do anything. Plus I couldn't get an erection and it killed my sex drive, and started giving me these awful headaches" "ahh OK we'll give those a miss then, maybe some propanolol" "Ooh sorry doc, no can do, they made me pass out when I stood up and gave me insomnia" "Oh dear, OK, well how about pregablin?" "Oh no no doc can't do that, those gave me indigestion" "well I would consider diazepam bu-" "Yeah! That sound great doc! I sure will try them!" They are likely to recommend SSRIs at first, so turn those down with an excuse so you don't have to wait over a month before trying a new one, but then no matter what the second one is its best to just try it and then go back after a week or two to say it's no good. It will be a work in progress for a while, but if you keep trying they will either prescribe you benzos or refer you to someone else.
Do you have any history of drug abuse on your medical record? If you do, this may be why you're finding it impossible to get benzos prescribed through the normal channels that the general public would use. Don't fret though, it just means you have to approach the situation in a different way, and you may even find this method helpful even if you don't have drug abuse on your record. If you find your local drug recovery agency and go and sign up with them and tell them that your main problem is benzodiazepines (make sure you have taken benzos beforehand so that you test positive for them every time you go). If you tell them you're addicted to benzos, they will get you to see a doctor there who's specifically trained for dealing with patients with drug dependency.
Explain that you're addicted to benzos that you've been buying on the street and that you want to stop but because you've had a seizure in the past you're scared to do it. Explain that you've been physically dependent for a long time, and that because your supply is tenuous you have often had to go through the start of withdrawal and it was awful, and that your dependency on the unstable street supply is severely affecting your work, relationships etc. They will prescribe you a maintenance dose of benzos - I think 20-30mg a day of diazepam is pretty common. The aim will be to get you off of them eventually, but if you just keep telling them you aren't ready to reduce yet then they'll keep providing you with the prescription. Once you've gotten stable the frequency of how often you have to go will be reduced and reduced until eventually you will only have to go once every 2-3 months.
Note with this kind of prescription they will not just give you a script for 2-4 weeks supply and send you off on your way, for a while at first it will be supervised consumption like they do with methadone & bupe where you have to go to the pharmacy every day and take the tablets in front of the pharmacist. It's a hassle but after a few weeks, provided you don't test positive for any other drugs (including other types of benzo) then your pickups will go from daily to every other day to a couple times a week and then eventually you will have a normal prescription. The advantage of this method is that whilst a regular doctor will only prescribe you benzos if you convince them that you've never taken illicit drugs and aren't abusing it, this kind of doctor at these agencies will only prescribe you benzos if you convince them you're already dependent on an illicit supply that you're buying off the street. As long as you stress that you're physically dependent, they are not allowed to turn you away without a script for a benzo, since they have a duty of care to everyone who signs up at the agency and if you were to be turned away and then a week later had a seizure from benzo WD that killed you then it'd be that doctor's ass on the line.
The main drawback of this method is that it will unfortunately mean that drug abuse will then be on your medical record, which will make it harder to get meds like opiates in the future and the hassle of supervised consumption. However it is much better to have a regular, ongoing, open-ended prescription for 30mg diazepam/day rather than a 7 day script of 6mg/day that they aren't willing to renew and can't wait to get you off. Just remember to take benzos before going so you test positive for them (if you test clean they aren't allowed to prescribe you anything) & it's a foolproof sure-fire way of getting yourself a diazepam script. Benzos are far from impossible to get prescribed here in the UK, you just have to be willing to either doctor shop and go through some trial and error and really work your doctors or go to a drug treatment agency and get drug dependency put on your record. The people claiming you can't get benzos in the UK either don't live here, haven't tried, or maybe just went to one doctors appointment, walked out with Prozac and then decided it must be totally impossible.