UPDATE 0946 GMT: Capcom have been in touch with us and informed us that the issue is resolved.
To download and install DMC, follow these instructions:
1. Launch Steam and log in.
2. Find 'DmC Devil May Cry' in your games library and delete local content, where possible.
3. Exit Steam.
4. Relaunch Steam and login, and then double click on DmC Devil May Cry to begin your 8Gb download.
As many of you will now be aware, there is an issue with the DMC: Devil May Cry keys. Many retailers, Green Man Gaming included among them, have received keys that do not allow users to correctly download and install the game.
We're in contact with Capcom to see a resolution to this issue and trust that you will all be able to download and install your game soon.