All nicknames can become given names in England and are often chosen for their non-pretentious, cute, 'warm' sound. In the toddler set now Charlie, Alfie, Sophie, Freddy, Frankie, Jack, Jake, Harry, Ben, Jamie, Katie, Ellie and Molly are all bestowed, quite popularly I might add, as given names in their own right. All are nicknames of other names in origin but, like other parts of language over time, their use has changed.
Debbie isn't so common now but in the 50's and 60's it was given as a full name. The practice used to be curtailed by religion where the baptismal name would be Deborah but the family might only use 'Debbie' from the hour of birth - they would still often record the more formal baptismal form of the name on the birth record. With only 8% of the British population describing themselves as regular church attendees now, such things often don't factor and the parents feel free to go with Alfie, etc. if that's the form they like.
One friend of mine named her now-1-year-old Frankie after her father. To this day, her father assumes that his full name, Francis, is carried by his grandson but the truth is, it's only Frankie on the birth certificate. His mother didn't really like Francis but thought Frankie was 'cute'.
Such names seem immature, cutesy or limiting elsewhere but it's rather common here in England and definitely on the rise...though like most things here, there are hidden class factors. To be succinct, Alfie isn't classy but Kitty is and Sophie may or may not be...don't ask me the hows-n-whys though, I do my best to ignore the class thing ;o)