When I altered a figure of 8 route to avoid repeating a road and added 20k to the distance my friendly local DIY organizer sent an e-mail back saying something along the lines of "the repeating roads stuff is internet bullshit, it's doing laps that's not allowed"
So from that I took:
Repeat roads are ok, provided it's not laps, exactly when a repeat road becomes a lap is down to interpretation of the person who will be validating the DIY or approving the route for an event, therefore if in doubt, ask them.
AUK regs, open to interpretation since 2000*.
* Apparently