After reading on some of the posts the debate about whether you should do some stretches before running - consensus seems to be it is OK to stretch after a run, I changed my normal routine where I have always done some stretches before my warm up walk. On Monday's run I did not stretch before the run just the warm up walk. As I neared the end of my 6 Km run I felt my right calf muscle beginning to tighten up. Later that evening I could hardly walk it was so tight, tried some massaging which helped a bit but the next day I was still hobbling around. The tightness was still there on Wednesday and had eased enough by Thursday when I was determined to run again, I did do stretches this time before my warm up walk then another 6 Km, of which the first 5 - 10 minutes were a bit painful but the pain eased off the further I ran. Later that day after the run there is still some tightness there but nowhere near as bad as on Monday. So I will stick to stretching both before and after my runs.
Not sure if that proves anything or adds to the debate but for me it looks like not stretching before a run is not good.