Went through the email us option on the contact us section of the O2 site.
Text of reply email below:-
I'm sorry but we suffered a fault with our data network due to which some of our customers are unable to access Internet services.
We've identified the cause of the fault, which relates to the allocation of IP (Internet Protocol) addresses needed to establish a data connection. We've managed to restore data services to the vast majority of customers and are doing everything we can to make sure the few remaining customers are back online as soon as possible.
I've also applied a goodwill credit of £10.00 including (Value Added Tax) and it'll be adjusted on your next bill dated 26 July 2009.