Hi, a gastrocnemius tears should be easy to diagnose using subjective tests and I would presume an orthopedic doctor should get that straight. If you want a more objective diagnosis of the extent of the tear then I would use tensiomyography (TMG), to compare the injured muscle belly with the healthy. The signs you describe are consistent with more severe tears I've seen in practice, although they usually respond well to rest, NSAIDS and therapeutic modalities I use in practice. I rely on TMG to manage my patients' recovery (mainly top athletes) and return to training timing. Unfortunately I'm based in Slovenia, I don't know who uses similar technology in the UK. Good luck!