What I meant to say about today's run was that it was rw according to my new pattern of walk of 40sec followed by fast run of about 30sec easy run building to brisk to complete the 4min cycle. That is it was for the first 3½miles but then my left hamstring felt as though it was beginning to pull so I cut out the fast bit and changed over to the walk followed by an easy to brisk run and that seemed to do the trick. The hamstring still feels a bit uncomfortable just moving about so I won't be trying to emulate Jo Pavey for a while.
Pattern: easy run 4min; *walk 40sec; fast run (near sprint) 20sec+; drop gradually to easy pace 1:45 ;build to brisk pace 15sec ; brisk pace 1min; repeat from * to end. Seems to be working, I'm surprised at miles 2 and 3 but HR is steady.