I used to have this app for ios, but it is now on Windows mobile and even better because it is free. It cost me about £25 on ios.
It is much more comprehensive than the Here Maps app. You can actually plan and edit your route. Along with other useful features.
Give it a go, it's free! Comes with 6 months free live traffic updates too.
Window Phone: There is, and always has been, a free app with the UK map. All in-app upgrades are standard price.