A very interesting read - thanks Rod Macarthur.

I am curious though: The lock without a key:
"The retaining wall of the high pavement in David's Road (pics 10a and 10b) beneath the Hob, is the side of a lock"

There is no historical documentation suggesting that there was a lock in this location. Other locks on this canal were marked.

The upper level of David's Rd (the proposed tow-path) seems fairly level with WHSmiths and beyond so there was no obvious gradient to overcome, (assuming the canal has been filled in to this tow-path level.)

(And Havelock Walk was named after the General - not a path with a lock.)

But then again, the ground at the site of the double lock at Honor Oak Pk Rd/recreation ground (now) looks level in the directions of the canal, so this is not necessarily a clue either way.

There is that sudden ~6 foot dip in David's Rd itself - a change of level consistent with a lock maybe? Certainly a strange feature.

It would be an interesting exercise to follow the path of the canal in SE23 with a (GPS?) device to see how level it is. That would give us a big clue whether another lock was needed or not.