from your description, it sounds exactly like a calf or Achilles problem. There are nerves innervating these structures and when they have small tears, they hurt. Try riding a stationary bike but put your arch on the pedal instead of the balls of your feet. Put a heel lift in both shoes, a small one, and do not try to force the muscle to stretch into healing. Once whatever is healed, it will be right but can be stretched only to the point of tightness. Hold it 60 seconds and don't bounce on it. Forcing it to overwork or stretching it to the max while it is healing will be counterproductive.
Think about it...if you sprain your wrist do you continue to bend it backwards or place heavy loads on it. You will be OK unless you snap your Achilles. With time you would known this, trust me. I played competitive volleyball and I did.

Go online and look up Achilles strains rehabilitation. There is a lot of good info on university sites, or at least there are here and I would have no reason to believe there aren't in the UK. We all have access to the same knowledge base.

Don't overthink it, take it easy, don't aggravate it, and work on your upper body and trunk. Most likely you will be ok