Ian, i think this session would be useful for either introducing some speedwork into your running if not used to it, or close to your race when tapering and still trying to retain some speed in your legs without losing fitness caused through a drop in training volume.
This session, through nature of the length of the intervals and length of the recovery, is largely targetting the anaerobic energy system. When running the half-marathon it requires about 95% aerobic running and relies largely on your ability to remove lactate.
A session to target this would be something like 6 x 1000m at slightly quicker than 10km pace, with 90 seconds recovery. This interval is long enough to accumulate lactate in your muscles, with a recovery too short to allow the full removal of it from your body....which trains your body to be more efficient in lactate removal, and hence you can maintain a higher speed for longer.
