Hello Mike,
I see Gunthar has already suggested this, but deleting the .blob file in the steam root folder forces Steam to check again what you have and don't have. So it might be worth a shot.
Also I would like to ask you to check within Steam options ( "Steam" -> "Settings" -> "Download + cloud" tab -> "Download region") what you selected as a download area (being in england, it should show UK-London or UK-Manchester). If it does but still fails, try setting another location near you.
It could be that Valve hasn't deployed the patch on all content servers around the world. Just an idea.