I'm planning on buying a Dell Inspiron 15. This will be used for surfing the web etc and also playing Football Manager. The laptop will have a 500GB hard drive and 4gb or RAM. For £382 I can get a Intel® Celeron® Processor 900 (2.20 GHz, 1MB L2 Cache, 800MHz FSB)but for £40 more I can get Intel® Celeron Dual Core T3000 (1.80 GHz, 800 MHz FSB, 1 MB L2 Cache. Which would be a better option?

Avoid the Celerons, get at least a Pentium dual core.

Why? Do u think I should pay the extra £70 for the Intel® Pentium® Dual-Core Processor T4200 (2.0GHz, 800MHz, 1MB cache??

Celerons are a dummy down version of a real pentium. They lack power to do gaming and video editing, if you want the cheap alternative go for it.

I don't know about the their notbook processor, but the new Celeron E3xxx desktop series are ok, they are basicly what a Pentium E5xxx desktop series were, now. Iron Sharpens Iron.