If you only got a budget of £150 then I don't think this can beaten for the price.
Asus GeForce GTX 560Ti DirectCU II 1024MB GDDR5 PCI-Express Graphics Card **BLACK FRIDAY SPECIAL DEAL**
Even with a good CPU etc no way that card with 1GB will play Ultra acceptably. Check the thread comparing 1GB and 2GB 560's in BF3!
IMO just scale back your requirements and use med / high settings. The game still looks EPIC.