This is an absolute improvement on 2012: mean score - 4.69 (Z=2.23) and 2011: mean score - 4.62 (Z=2.47), when Oxford equally topped the table.
The National Student Survey is an on-line survey offered to all final year students in all degree courses in UK Higher Education Institutions. The survey consists of 22 questions. Respondents answer each of the 22 questions on a five point Likert scale from 1 (definitely disagree) to 5 (definitely agree). Results for the NSS 2013 were published this morning and can be downloaded from the HEFCE website here.