In reply to nniff:
> (In reply to brt)
>
>
> My apologies - I think you're right - it's not what I was told many years ago. We live and learn,
>
> Still prefer a steppy-through bowline for tying into the middle of a rope to lead or second though, whatever you want to call it, and indeed for a waist tie too.
That's a bowline on a bight - ABOK # 1080, p 195. A good knot for this solution.
As for escaping the system: one assumes that tying into the middle is done because we're on a single pitch crag and using just one half doubled up. The leader tying into the middle would create a little more faff but not unsolvable given some thought and how likely anyway?