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and download of Wales completed in about a minute. Thanks@Tony-13, It's not that difficult, although I am unsure how you managed to get 2 download processes simultaneously.
If you think Germany instead of UK you will see this if you go backj into the menu - offline maps:
If the checkmark on the left is visible, all is okay. If not, you can klik the > to enter the UK regions. There will be a down-arrow on the right. With that you restart the download. It will take some time to index the parts you already received, but after that it will continue your download where it left off.
In the end you will see something like this:
Checkmarks for all regions, and only a X on the right. Don't press it, it will delete your download 
Sometime a download gets stuck. In that case a force-close and restart of the download as described above will get you going again. Try to leave the phone untouched until the download is ready, and seek a spot with good wifi reception. Yes, all in all it is a bit finicky indeed...