I was sent a link to this website http://newintervaltraining.com/
This is an interesting site with an introduction to a slightly different way of running interval sessions. The gist of the difference is that the hard efforts should be at a slightly slower pace than in a traditional interval session, but that the recovery phase should include an “active roll-on recovery” section. The intervals may be split into sets to make it more feasible to complete the session.
It is used by a number of highly respected coaches and appears to be effective.
There is an interesting discussion here. The author points out that these types of intervals have been done for some time by certain athletes, so may not be anything new. That said, they are definitely worth thinking about.