I understand that you have some questions about the Slingbox PRO-HD and some of its features.
1) Will the Slingbox Pro HDs internal tuner currently be able to recieve freeview channels in the UK?
Short answer is yes. The Slingbox PRO-HD allows you to receive the TV signal provided by Freeview in the UK.
2) Does it have the capability to learn IR codes for my devices if the codes aren't available out of the box?
Yes, as a matter of fact, there's an article that explains how to:
3) I see two versions on the internet - a red one and a grey one. Is the grey Slingbox the current and most up to date model?
Right. While the Slingbox PRO (red one) allows you to connect up to three devices, it does not allow you to stream a HD signal. On the other hand, the Slingbox PRO-HD ( gray one) allows you to connect up to three devices and you can stream the HD signal. The Slingbox PRO-HD is the top of the line model.
The following links will provide you with all the information about the Slingbox PRO-HD:
Hope this helps.