What has changed?
Previously a search on Google would yield a map result of the area, such as this:
From this it’s not obvious the exact area of the map the postcode relates to, though we can assume the centre of the postcode area is at the centre of the map. Now, however, we are presented with a more exact outline of the postcode area:
This also works for zip codes in the USA:
Note, however, that at the moment I am only seeing this when searching on Google UK. If I search on the .com domain I don’t get these outlines. This is more useful information from Google that I’m sure will be rolled out across all domains soon.
Note also that this doesn't work in Google Maps itself yet, only on Google search. You still need some sort of hack to get postcode outlines in Maps.