This is what London would look like without the Thames Barrier, according to the disaster novel 'Flood' by Richard Doyle.
I set off without a nautical map - just an old ordinance survey one, from before the O2 was built. The next stage was through the Thames Barrier, past the Woolwich ferry and on until Erith Yacht Club.
But I was right in front of the barrier, so I called again: "I am right in front of the barrier." "You are cleared to go through now" "Roger that, thank you and out." Calm voices throughout.