quitting a phd

Hi, 
For the past 4years I've had a position in the uk as a research
assistant that included a part-time phd. My research assistant
contract has now ended and, to be honest, I can't see much point in
carrying on with the PhD. I don't feel that it's going anywhere and
I've no interest in going into research after this.  Being a member of
staff, the fees for the PhD were waived. I now want to know what the
consequences of quitting would be. Will I be expected to pay back any
of the costs? Will I be able to walk away so long as the terms of the
research contract are met (relatively easily done by submitting a
formal report to the funding body)
Any help would be greatly appreciated. 
Thanks, Doug