Google announced they have finally switched off their third-party maps data provider in the UK and is now powering the UK maps with their own data. They've done this in the U.S. and other countries and now have made the switch in the UK.
This applies for the UK, Germany, Finland and Sweden. How do you know if it is Google Maps data and not a third party? It says so on the bottom:
You may notice many improvements to Google Maps in these countries, such as improved water bodies and more comprehensive local park coverage. Many of these and other changes are the result of us working directly with a variety of organizations, agencies and data providers. For example, Germany's Federal Agency for Cartography and Geodesy (Bundesamt für Kartographie und Geodäsie) supplied us harmonized data from surveying and mapping agencies of all 16 federal states (Länder). And in the case of Finland, we acquired water body data directly from the National Land Survey. We're thankful to these and other data providers for helping us ensure that our digital maps accurately reflect real life.
Also, now when you see an issue with the map data within the UK, Germany, Finland and Sweden you should click the "report a problem" link.
Forum discussion at Google Maps Help.