Smear Tests

Jess • I'm Jess. 31 year old teacher and cat mum. Single.
Hi everyone, I hope you don't mind me asking for some help. 
Does anyone have any advice for handling smear tests when you have experienced sexual assault in the past?
I have had one successful smear test in my life which was performed while I was under general anesthetic for a different procedure. I can't comprehend how I will ever cope with being awake for one. 
I'd tried before and I've tried since but the second the nurse touches me I lose all rationality and become extremely distressed. Last time I tried was about 9 months ago. I took my best friend with me who is also a trained counsellor. But it didn't work. I've had psycho-sexual Counselling and CBT but I feel like I'm just banging my head against a wall. 
I am at a loss. I'm 30 and now 2 years overdue for a test. 
Should I just pay privately and ask them to knock me out (will they even do that?? Is it ethical? Irresponsible?). I'm in the UK so smear tests are free on our National Health Service but for a bespoke procedure I think I'd have to find a private practice. 
So, so, so grateful to hear your thoughts.