Stiff Upper Calf (both legs)

Just a general enquiry about recovery plans for strengthening sore calf muscles.

I have been running for over 5 years, nothing too serious, about 3 times per week, a mixture of on & off-road, on both flat and steep ground, but usually no more than 5 miles per run. I have never had any running injuries, and not a hint of any muscle strain in my calves. The only injury i have sustained was a nasty muscle tear to my lumbar region in February caused by lifting a motorcycle whilst my back was twisted, but after physio I was back running without any problems within 5 weeks.
However, after returning home from a recent hill scrambling holiday in Wales about 6 weeks back (walking & scrambling around 20 miles a day), I felt a twinge very deep in my left upper calf muscle bounding up my stairs at home. This was followed the following day when the right calf pulled whilst out walking. Neither 'pulls' felt that serious to be honest, just a twinge, which I thought was probably because I wasn't used to walking those distances, or scrambling up rocks every day. I thought the problem would get better after a few days, but 6 weeks down the road, I'm not sure how to get back to full recovery.
The problem seems to randomly appear after walking, and not necessarily walking very hard. For example I walked around 15 miles in the Derbyshire Peaks two weeks ago without any problems, but then slightly pulled both calves again yesterday walking less than half a mile to catch my train? I have been running (very slowly & only a few of times in the last 6 weeks), where after an initial feeling of stiffness/soreness for about a mile, my calfs become 'normal' for the rest of the run. After running, I feel tightness afterwards, and some discomfort going up on my toes, but seem fine the following day.
I really want to get back to full fitness, so any advice/recommendations for stretching/resting/or whatever would be useful.

Do you mean that you are experiencing a muscle spasm, or that you feel that you have generalised tightness, or an actual muscle tear or strain, or tendon issues?

Thanks for replying. The feeling is like a knot appearing in the Medial Gastrocnemius. It initially occurred due to overuse (a few days after climbing up the north side of Tryfan which is pretty vertical). However, it will now come on suddenly during exercise (seems to happen on walking if I go to fast), with the tightening appearing later as a tight band across the same set of muscles. This subsides after rest (like a nights sleep). All may be well for several days, I may even exercise without trouble, only to happen again in either the left or the right, but not always at the same time. The initial feeling is like a very sudden twinge in one small area. (for instance in my right calf this would be about 3" below the back of the knee to the right (inner side). There is tenderness if I press down hard into that area.

Sounds like you need a good deal of myofascial release, combined with biomechanic assessment and subsequent management of the joint. Your muscles are protecting your joint from real damage, best thing to listen to it and get some hands on work for that calf.