Just phoned up John Milton who lives alongside Stanstead Lock and he tells me that boats are moving through, albeit under BW escort because of all the paraphernalia they have yet to dismantle. So (fingers crossed) it looks like we're OK to head southwards on Sunday.
The answer (as promised) to the quiz question about average speed of underground trains is 21 mph. My original guess was 20 so I was pretty close. However Kath persuaded me to reduce it to 14 so it just goes to show something!