Came back twenty minutes later and it had gone...stolen...nicked.
Went home and as I need a bike like other people need shoes, went online to Gumtree and agreed to buy a replacement bike, to be collected from away down in the East End by the Royal Docks.
On Saturday, strolling past a busy barbers shop two street away from where I'd lost it, there it was. I checked it out and everything was intact, so I stole it back...
Sunday I set off to get the other bike (I'd promised to buy it) a tenuous journey via a replacement bus for the first leg of the District Line (Underground) to Tower Hill. Then the Dockland Overland Light Railway (to give it its imagined title) to the Royal Albert Dock.
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Now I have two bikes so I'll have to keep the new one for Sundays...