I have now done the 5k improver plan on Run Double twice now. It is a 3 mile interval run which for the first 4 runs is 300m running and 100m brisk walk then the next 4 runs are 400m running and 100m brisk walk etc, etc. The first time I did it I pushed the running sections trying to get under 10 min/miles and jogged the walking bits which was a mistake as I didn't complete the 3 miles. I knew I had really pushed myself though cause my muscles have been sore for the last couple of days.
Tonight was my second run and I was determined I would run the full 3 miles and push my pace but decided I was to do the brisk walk instead of jogging. I did a pace of well under 10 min/miles completed the 3 miles and am so chuffed.