Found it for £36 from greenmangaming so you'll just get a key on release date, enter it in Origin (hopefully, doesn't say otherwise)
use the 20% off code: GMG20-FDSCL-AQQXD to get it for £36, £33 after cashback (quidco/topcashback etc)
http://www.greenmangaming.com/s/gb/en/pc/games/shooter/battlefield-4/Edit: Just pre ordered it from GMG:
"Battlefield 4
Activation Instructions:
Keys will be delivered by the release date of the game.
1. To activate your game through Origin download and install the Origin client.
2. Create an account with them, or log into your existing account.
3. Open the settings menu and click Redeem Product Code
4. Copy the code from your GMG game page and enter it. Some titles may send you to a different URL to activate the game – use your Origin login here."