From the Holloway Odeon down to the Angel is the longest run of free wi-fi in London, and you’ll be able to access it from any of the many bars and cafés on Upper Street. Look for the StreetNet network, register a username and password, and you’ll be given a one-hour session which is renewable as many times as you want (you’ll just have to log back on).
The Square Mile is as a wi-fi-enabled zone, but it’s not free. The network is run by a broadband company called The Cloud, to which you have to pay a monthly subscription. It is free, however, for all owners of an iPhone, or anyone signed up to an O2 broadband package. The Cloud runs a similar network in Canary Wharf.