Many free web-based email services don't support the POP3 or IMAP protocols (which is what Outlook uses). However, to the best of my knowledge, all email services provided to subscribers by UK ISPs do support POP3. Some of them also support IMAP.
Sky mail supports both POP3 and IMAP. Sky recommends configuring Outlook for IMAP, as this offers greater reliability and flexibility. Instructions for Outlook 2007 are here: http://tinyurl.com/skyoutlook2007