Having just come down the Nene from Northampton to Peterborough I have to say that although the majority of the Guillotine Locks are now electrified, the unsuspecting (like me) can have problems at the MANUAL locks!
Although one has to accept that it needs around 190 turns of the wheel to raise (and lower) the gate, having released the locking pin to 'free' the wheel (using the EA key) there seemed no way to get the locking pin back into the wheel after use, or indeed to keep the wheel from unwinding of its own accord. (decapitation came to mind)
Unfortunately, there were very few people about in early October and I have to say that evenually, some kind person who had also been in the same predicament showed us how to do it, after haing phoned the EA
For the benefit of anyone who is making this passage for the first time therefore, THERE IS A SMALL FINGER HOLE AT THE BACK OF THE METAL BOX CONTAINING THE KEY AND BOLT MECHANISM. You just need to push the bolt back against the spring (into the hole in the wheel) and then push the lock back in place.
PHEW ! I said my piece and hopefully it will save others the stress of the problem.
Pete