Jim

According to this: Blackout, Due to the high road casualties in 1940 the speed limit for motorists was reduced to 20 mph during the Blackout. Central white lines were painted in the middle of roads (which are still with us today) and curb edges were painted white as well. Kerb finders could also be used which were attached to a walking stick or umbrella..

And here: Life during the blackout, there's a picture of women white-painting.

As Terry said, there were white lines in England earlier, but I don't know how extensive they were.

Mick