Jinny, if I can give one piece of general advice, it's not to assume anything (in terms of how you will react to a med) until you've tried it.
To correct a few things...
> I absolutely agree, i think i have either endo or adenomyosis...i have raised this countless times with my GP, who tells me the only way they could find that out is by doing a hysterectomy "and they won't do that as it's a major operation, they are drastically reducing the amount they carry out because it's high risk and you'd have to wait for ages for one anyway..."

Sorry, this is total crap. I think you need to change doctors or change practices, especially if you want a decent standard of care and you're not going to go private.
Are you sure she said a 'hysterectomy' and not a 'laparoscopy'? The gold standard for diagnosing endo is a laparoscopy. This is keyhole surgery where the surgeon looks and gets eyes on all the organs, to see if he can identify endo. There is a 'diagnostic lap' and a 'treatment lap' - but if a surgeon is going in there, and you are under GA, they may as well treat anything they see. Otherwise you'd have to go back for another surgery. I went private for my lap back in 2013 because I was leaving the UK and at the time the waiting list was 9 months, so I was going to get caught between 2 health services. I had surgery 5 days after my initial appointment with a surgeon, privately - and he gave me a treatment lap for the same cost as a diagnostic lap. (It was about £3K, back in 2013.)
The other thing to say about laps generally, is it's important to see an endo specialist - because often endo is missed if the surgeon doesn't know where to look or how to identify it. You have the right to have surgery anywhere on the NHS so would need to research where to go, in FB groups for endo - whether in the NHS or privately.
The gold standard treatment is also excision surgery, where they cut out the endo they find, at the roots. This takes more surgical skill and someone who knows what they are doing. The less effective treatment is for it to be lasered out. This leaves the roots and it typically just grows back again.
HOWEVER, I would say - before you go down the lap route - it is really promising that these symptoms go away when you take the utrogestan, because it means the endo will be controlled and suppressed if you can just find a decent progestin which works for you and doesn't give you the side effects. YOU REALLY NEED TO LEAVE NO STONE UNTURNED. That means - try everything.
>I suffered terrible depression in my 20s from taking the pill, so have refused Mirena (which they push with great gusto....as it also means you hopefully go away for quite some time)
I would not assume that you are going to get the same symptoms from the Mirena. The pill is designed to be systemic and it affects every organ in the body. The tiny dose of progestin in the Mirena is supposed to stay local to the uterus and not go systemic. Research shows that in the first few months it is in, it does release more progestin and you may absorb more systemically - but then this reduces.
My concern with the Mirena would really be that it doesn't control the endo - simply BECAUSE it is local and not systemic. Who knows where your endo is... It could be on bowels, bladder, etc etc. And progestin in your uterus is not necessarily going to suppress endo anywhere else in the pelvic cavity.
Have you tried desogestrel? It is a mini-pill which is licensed to be used alongside HRT and (off license) can be used as a progestin with HRT. In the studies concerned, they used double the mini pill dose - but I'd think even the regular mini pill dose would be sufficient, along with an ultrasound after 6 months to make sure your uterine lining is thin under that regime. (You may need to pay privately for that ultrasound.)
Desogestrel is available (for contraception) without a prescription now, so you don't even need your GP's consent or prescription to try this. Frankly, I am so over NHS GPs by this point.... I would try desogestrel at the mini pill dose and see how that goes. By 6 months, I would get a private ultrasound to check uterine lining. Keep getting the utrogestan from the GP along with the estrogen, just don't take the P.
See here, in that link I gave you above:
" Earlier studies have reported that desogestrel 150 micrograms is effective as the progestogen component
of HRT with no increase in the risk of endometrial hyperplasia.33-34 There is lack of evidence on the use of
desogestrel 75 micrograms as the progestogen component of HRT. If desogestrel 75 micrograms is used
as contraception in women receiving HRT, it would be recommended to add further progestogen (e.g.
Utrogestan 100 mg daily or 200 mg for 12 days a month) to provide adequate endometrial protection."
75mcg is the regular desogestrel dosage for mini pill and 150mcg is the doubled dosage they've used for HRT studies and found to be fine. (They just didn't use enough women in the study to make it viable as a licensed alternative). But all women are different. I was on desogestrel after my lap surgery for 10 years and it very successfully suppressed and controlled my endo all that time. I also didn't bleed at all.
There are other options for progestins in that list.... Work through and make sure you've tried them all. Anything which says it is 'licensed', is something your GP should readily agree to prescribe you to try.
Hope that helps...