That's just it though. I don't think there will be much divergence, just a rewind to a less extreme time more akin to the Osborne/Cameron austerity govt than new labour or anything approaching left wing.
Progress has to be measured from where we are now, not past high watermarks.
If we're heading into bad economic times then what Labour can do will be restricted, but it's also when they make the biggest difference compared to Osbourne and co gleefully slashing at any and all public spending they can.