There are some choices if you're willing to increase your budget to upto £500. I think £450 is just too small a budget to expect reasonable performance.
In case of Starcraft and WoW you'll have to sacrifice some settings but you will see above 40fps in some scenarios
1) From
Overclockers.co.uk CPU i3 3220, AMD 7850, 500GB HDD, PSU Cooler Master Elite 500W, 8GB RAM ~ £480 (includes shipping)
2) From
Aria CPU i3 3220, AMD 7750, 1TB HDD, PSU Corsair CX 500W, 8GB RAM ~ £480 (includes shipping)
3) From
Scan CPU i3 3220, AMD 7750, 500GB HDD, PSU Corsair CX 430W, 4GB RAM ~ £480 (includes shipping). NB make sure you customise this build and choose the 7750.
Now i've ranked them in terms of performance, although 2 and 3 are fairly close. The only thing which limits your FPS in those builds is the CPU, but thats only WoW tbh. Number 1) should handle quite well @1080p.