If you have the 'ok, notify me' message when clicking the icon Run command prompt as administrator and enter in "wuauclt.exe /updatenow", this should start the update :)

Are you in the UK by any chance, as maybe it's a regional unlock?

$Windows.~BT folder has downloaded 5.64GB in the last couple of hours and has now stopped, but still no installation message. Any ideas as to how to initiate installation as when I click on the GWX...