Earlier quoted context omitted.
The point here, though, is that it doesn't matter whether the driver could've seen them, because culpability rests with the driver by default (except, as mentioned, in situations such as motorways, where pedestrians aren't allowed). In very general terms, as a pedestrian in the UK, you have no particular right to step into the road other than at marked crossings, but as soon as you do, you have total right of way, no…
I'm sure it works fine in practice, but it's still not ideal if you can put one foot into the street and oblige cars to slam on their brakes.
This is independent of legality. I'd hope that it'd be the case even if laws were passed that explicitly punished braking in such a scenario.
Anyway, in the UK, it's illegal to walk down the side of a motorway. But basically anywhere else is free reign for pedestrians.
People don't generally walk out in front of (fast moving) cars because they're not suicidal.
In a place like London it's fun to watch (and take part in) the stand-off between cars and pedestrians though.
I womble through crossings all the time. The lights are advisory for pedestrians. They're designed that way; the green man exists for the elderly and children.