Whoops!

This is how not to treat the drivetrain on your bike. I've mentioned before that the Brompton needs a new chainring, sprocket and chain and this is why.

If you don't change your chain regularly the pitch of it changes and wears everything else to match that new pitch so a new chain won't fit or will prematurely wear. In the extra photo, taken with flash, you'll see how badly the teeth have worn so that a new chain doesn't even mesh in the sprocket.

Having said all the above, this drivetrain has done ten years sterling service, through thick and thin, but I've been lucky to get away with it this long and if it wasn't a hub gear then I wouldn't still be riding it.

Good old Billy Brompton!