I also had a partial S/L tear a few years ago. I didn't have any surgery and the recovery time was about 6 months-ish, but I irritated it again after about 3 months, similarly to you, catching a hold. It now seems to have recovered fine apart from some random mild aching on the radial side of my wrist that isn't in the same area.
After reviewing my MRI with a wrist surgeon I'm not really convinced that S/L tears show well on MRI, although mine didn't have contrast dye. Apart from MRI, the sign of S/L rupture is whether there is static and/or dynamic instability. Fluoroscopy can be used to see if there is a widening of the S/L gap on movement, but it doesn't seem very popular in the UK. Widening of the S/L gap also shows on x-ray, but the images need to be taken by some one with experience of S/L injuries as the wrist needs to be put in a position that pulls the scaphoid and lunate apart.
As I'm sure you know, untreated complete S/L rupture usually leads to SLAC wrist after a few years, quicker with heavier use, for which only some kind of fusion seems to be the treatment, so it would be worth getting a second opinion or having further investigation if complete S/L rupture is a distinct possibility. That said, repair of the ligament is only possible for about 1-2 months post injury, after which time reconstruction of the ligament is the only possible solution. S/L reconstruction is a fairly major operation, that doesn't always lead to a good outcome. It also can't be left for a few years to have at a later stage as it is contra-inidicated if there is any sclerosis. The surgeon I saw said he wouldn't consider operating if you are capable of press-ups without pain. All in all, it's a bit of shit injury, so I'd hope that you've not done that.
Gold standard diagnosis is only possible with a scope. I reckon most wrist surgeons would suggest that as a next step if you are still having problems.
I find the NHS is terrible for taking orthopaedic injuries seriously unless you can't work, although you may have more luck as a medic. I can recommend Mike Hayton in Manchester if you want to see someone privately. He has a practice that is entirely limited to wrists and hands, he specialises in sports injuries and although not a climber is interested in climbing injuries. He also has a specific interest in S/L injuries. I can't think of anyone better in the UK.
Disclaimer - not a doctor, but apart from having had a wrist injury myself, I do medico legal work, have done cases involving failure to diagnose complete S/L rupture injuries, had conferences with a number of experts, and have a good friend that is a hand surgeon in Canada that I have irritated with endless questions.