I had the misfortune to suffer from one of these about 20 months ago, pain was excrutiating and onset was without warning - hence you will almost certainly have your medical temporarily susupended. The pain is the nearest a male will get to experiencing childbirth apparently
Like you, my stone was lodged in the ureter and of a similar size - too big to pass naturally. None of the options for removal are pleasant. My urologist convinced me to go for the rigid telescope and l@ser option which promised just about the quickest route to recovery of the medical. I won't go into details but I'm glad I was fully unconscious. Unfortunately the first attempt at lasering the stone was unsuccessful and I had a 'double J stent' inserted. This small tube hooks into the kidney and bladder ends of the ureter - it's purpose is to ensure the kidney can drain urine past the stone to the bladder. A blocked ureter can cause the kidney to die! I now know what to wish for for my enemies - for the 4 weeks it was in place the double j stent caused the most discomfort I have ever experienced. Every pee was a punch to the kidney!
Still reading? OK the second attempt at lasering was successful and for the next 2 weeks I had to pee in a jug and then sieve the contents for the shrapnel. Consultant was happy with small collection of remnants - all about the size of a grain of sand and not at all painful to pass.
A final IVU X Ray to confirm stone had gone, sent details to CAA and medical category restored. Total time from onset of first symptoms to restoration of medical was about 12 weeks - this would have been about 8 weeks had first l@ser attempt been successful. I now have to do further IVU X Rays at 2 and 7 years from anniversary of episode to maintain my medical.
The CAA website has a useful flow diagram which explains all.
Best of luck!